For Pathfinder, as mentioned in the comments above, Crossbow Mastery is pretty useful. Otherwise, as far as feats go, you've got 'em covered.
The Far Shot feat will turn the -2 range increment penalties into -1, which can be very useful to shoot from long range.
Here's where some cheese comes in-- when you take a 1-level dip in Rogue with the Sniper Archetype, you gain the Accuracy ability, which that further by half. This does stack RAW, which effectively doubles your range increment distance before you even see a penalty. For example, you can pick stuff off from almost half a mile away with only a -4 penalty. Granted, you'd need scrying or something to spot your targets, but your stealth check gets hilarious... Your GM will probably scowl at you for this. Pay him back by taking Leadership and Siege Engine feats... and chuck donkeys at the BBEG from the next county. On a more serious note, the Ballista is good and can be used every turn like this.
If your GM allows material from 3.5e, then you can take both Crossbow Sniper and Improved Crossbow Sniper. The former grants you half your Dex modifier to damage and a +30 feet to Sneak Attack and Skirmish ranges, and the latter bumps it up to full dex and an additional 30 feet. Furthermore, a 1-level dip in Rogue grants you a Sneak Attack, and the Craven feat from 3.5 will grant you your character level as bonus damage to SAs (at the cost of -2 will saves against fear effects).
If your GM will allow things from 3.0, you can attach a Gnome Crossbow Sight to your xbows to ignore the first two range increment penalties.
As a GM, I allow pretty much all things regarding crossbows in Pathfinder, because they're already such a sub-optimal weapon compared to bows, thanks to the absence of the strength modifier to damage and manyshot. You'll probably be using the Launching Crossbow as an Alchemist, so your experience won't be as bad as most classes, but the feat tax for using any crossbow is almost ridiculously heavy.
A little bit more cheese, but if you take a 1-level dip in Oracle, choose the Waves mystery, and take Water Sight as your first-level revelation, you'll be able to lay down Obscuring Mist a few times a day and be able to see through it without penalty. Being able to shoot with guaranteed total concealment is a huge plus to tactical fighting (its the basis for my Sniper using crossbows in my current PF game, in fact, since the concealment guarantees Sneak Attacks)
The best way that I can see you improving your combat effectiveness is through the specific spells you choose.
As you had said, money is sort of tight in your campaign, so you need to make due with what you have at your disposal naturally. Luckily, this isn't hard considering that you have a +4 Cha score (Giving you anywhere between 1-4 additional spells per day at your current bonus). So considering your want to improve how well you do in combat, focus on preparing combat buff spells
These are the spells that I think you should prioritize (keep in mind that I only have the core rule book on hand):
+Bless Weapon(1st): A very situational buff, but powerful when used against the right enemies (ya did good on this one)
+Magic Weapon(1st): Prepare this instead of Bless. Bless may give you a bonus against fear, but Magic Weapon increases your damage as well as your attack bonus.
+Bull's Strength(2nd): I know that you put most of your stuff into Ranged Weapons, but everything on the list available to me is either a buff you don't need or something that seams too underhanded for a "rock star" (also, I don't think you need a spell that lets you take half of the damage that your friends take when there is a fully-functioning tank). As you may already know, Bull's Strength increases your Strength Ability by 4, so at the very least, you increase your Combat Maneuver Scores. This means it's easier to absolutely wreak an enemy's day by affecting how they move, inflicting statuses on them, or simply moving through them.
+Greater Magic Weapon(3rd): THIS is one of the key spells you should prepare when you get into the upper echelons. It's like Magic Weapon, but it gives you additional bonus amounts for every four levels your character has. Also, this spell specifically states that you can cast this spell on up to 50 arrows in the same quiver; this means that if you have to switch to another bow, or if your party also invests in bows, the spell is used to its maximum potential between multiple weapons.
+Prayer(3rd): Anyone in a 40ft radius of you receives a +/-1 to every roll depending on their loyalties; That's an increased advantage of 2 against whatever enemies you are fighting!
+Dispel Chaos/Evil(4th): these two spells give you +4 against the attacks of the designated alignment and automatically dispels effects cast by said creatures or spells that are of that alignment
This last one is just in case you attempt to build physically or your Fighter is being cornered by a Demon or something...
-Holy Sword: PROS: weapon automatically becomes +5 AND deals an additional 2d6 damage to Evil Creatures. CONS: Can only be applied to melee weapons and negates the powers of whatever weapon it is used on (that last bit could be fun to use against an enemy using an all-powerful cursed weapon, but again, this is a bit situational)
I hope this helps.
P.S.: Your party should invest in Heavy Repeating Crossbows once you hit level 10
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Best Answer
Yes, Deadly Aim is worth it.
The math in Pathfinder tends to work out such that people who want to attack tend to have a bit too much attack bonus—and need ways to turn their extra attack bonus into damage. Many, many features revolve around doing that.
For example, most archers also use Rapid Shot, −2 attack penalty for an extra attack.
But ultimately, archery is a combat style with a lot of extra attacks, but tends to struggle with actually getting significant damage on those attacks. Deadly Aim adds damage to every one of those attacks, which is what makes it worth it. And archers are often full-BAB, and should go all-in on Dexterity. They should have plenty of attack bonus to spare.
Trying to switch weapons, however, is not.
What isn’t worth it is the greatsword, or the 18 Strength. If you absolutely must have a switch weapon, make it something you can finesse, and then take Weapon Finesse—except don’t do that, because it forces you to split your feats and your wealth and you just end up sucking at both melee and range.
There is basically zero reason for an archer to switch to melee anyway: unlike a melee character who can be faced with an opponent you can’t reach, a ranged character can always attack. You do provoke attacks of opportunity if you are too close to an enemy when doing it, but in my experience, it is a very rare case where you cannot simply take a 5-foot step away from enemies, and then fire away. Even when you can’t, switching weapons would take your entire turn—if you are going to waste your entire turn anyway, you might as well just reposition so you aren’t in harm’s way and can utilize your feats and class features optimally. Expending very scarce, very precious resources (ability scores, feats, thousands of gold, actions in combat) for such rare scenarios is not a winning strategy.
Also, getting Strength just for the damage bonus on ranged attacks isn’t really worthwhile. You’ll probably have a certain amount of Strength just to carry your gear, and I’m not saying you should ignore the +1 or +2 you get that way. What I’m saying is that an 18 costs far too much for what is, at best, a fourth-rate concern (after Dexterity, Constitution, and Wisdom), and magical items to improve Strength should be very low on your list of priorities (to the point that you’ll probably never bother to get them).
Which leads me to a broader, more important point:
You cannot afford so many ability scores
Pathfinder absolutely does not support characters who care about more than two or three ability scores. You need Dexterity to hit with your archery and to qualify for archery feats, and you need Constitution to not die. Some Wisdom would certainly be good, too, considering the existence of ranger spellcasting; you might be able to manage a bit there (certainly at least the 14 minimum you need to be able to cast all the ranger spells, but hopefully a bit better than that by the time you get high enough level to worry about them).
But adding Strength to this is only going to hurt you. You will pay far, far, far too much trying to keep everything up to relevant values, and you will suffer immensely for it. Note that the game’s math assumes you do have the latest and greatest enhancement bonus to your attacking score rather soon after it becomes affordable, and that the game chargers you 50% extra to get an enhancement bonus to a second physical score—you will, by definition, be unable to keep both Strength and Dexterity high enough to actually hit things.1 Pathfinder very simply does not support the kind of character you want to make.
But what about all of these problems that might happen?
All of these concerns are real, but many of them are not actually a part of Pathfinder, but rather things that your GM has house ruled. I would, generally, recommend strongly against a GM doing any of those things, both the house rules and the pedantic implementation of the official rules. But nonetheless, if that’s the game you’re playing, you have to have answers to them.
That doesn’t change the fact that the greatsword is a poor answer to them. Quick Draw only covers drawing a weapon, not sheathing the previous one, so you either waste an entire turn—and therefore might as well have just repositioned—or else have to drop your first weapon, which sounds like an excellent way to lose it. Losing a magic weapon can cripple a mid-to-high-level character; even as early as 4th or 5th level the game just punishes you massively for not having one. (Actually, it can do that as early as 1st, even though it’s generally impossible to have a magic weapon at 1st.) And greatswords still suck underwater, and eventually you really want some form of freedom of movement anyway.
But you can get around some of the issues if you’re clever. The name of the game is to protect your investments, rather than trying to diversify.2 That is, don’t try to use a Strength-based greatsword and Dexterity-based longbow, use one weapon, and one ability score, to do both things. And to do that, you should
Seriously consider throwing weapons
If you really want to excel both in melee and at range, don’t use two weapons, use a weapon you can throw. Use Weapon Finesse—or better, save a feat by using effortless lace—to make the weapon use Dexterity for attacks even while in melee, so you don’t need Strength. Use a blinkback belt, and ensure you always get your weapon back—whether you threw it, or dropped it because of the absolutely atrocious houserule about dropping weapons on a 1. Unlimited ammo, because you just keep on throwing the same weapon over and over.
If you really want, you can have a throwing sword. You can’t use a greatsword since blinkback belt is limited to one-handed weapons, but you could have a longsword.
And you build that character mostly like an archer, probably. You pay an extra feat for Quick Draw, and your range is limited (you might want a second feat for Far Shot, though it doesn’t help as much as it should), but it gives you a fallback option for when you absolutely cannot attack at range. Hopefully some of your feats, and all of your weapon bonuses, apply to those melee attacks. Deadly Aim is still worth it—and Power Attack isn’t, because most of the time you’ll prefer ranged attacks, the melee option is just for emergencies, and for low levels before you can afford the blinkback belt.
(And if you really cannot find basic gear like this in your campaign world, someone in the party should be crafting. Crafting is a massive advantage even in a typical Pathfinder game; in a game like this where you can’t just find things, it becomes absolutely crucial. That’s not even metagaming, if you live in a world that relies on magic but it’s hard to find, every serious adventuring group would make sure to have someone who could provide it.)
About the game overall, or, seriously consider just being a sorcerer
But really, it has to be said: your GM is applying a ton of house rules that very, very negatively impact mundane, martial characters—already the weakest characters in Pathfinder. Dropping things on a natural-1, the inability to find or even make relevant magical items, these are major departures from how Pathfinder works. For that matter, going after weapons and meticulously tracking ammunition are things most GMs just don’t do—because, as I said, Pathfinder martial characters have enough difficulties without actively trying to screw them over.
I don’t know all the details of your game. I don’t know if there are also changes to magical characters, that even things out again, and I don’t know if there are adjustments to challenges and monsters to make them workable in this setting. Hopefully there are. But from what I’m seeing, these rules make the game so antagonistic that you are all-but-forced to choose absolutely self-sufficient characters. Which means, I guess, everyone should play a sorcerer always. Nothing to steal or break, no absolutely mandatory equipment to just not have, no god who can arbitrarily decide not to give you spells that morning. Which is precisely why these sorts of house rules are so heavily recommended against: the natural response to them is to just avoid the classes that are getting shafted, and gravitate towards the classes that can avoid them. That reduces the diversity and variety in your game, and that’s generally seen as a bad thing for the game. Most GMs try, instead, to bolster martial characters, to make up for their systemic shortcomings, and instead try to reign in the spellcasters, who are far too powerful to begin with. By doing the opposite (again, if that’s what is happening—I don’t know what other house rules are in play), you end up instead just making it that much more beneficial to just stick with the overpowered classes.
Note that I strongly recommend ignoring this rule entirely; it’s absolutely awful. Ultimately, though, even without the 50% surcharge, you still can’t keep both scores up, at least not without doing something disastrous like having suicidally-low Constitution or ditching what is actually your strongest class feature, the spellcasting that needs Wisdom.
I am not a financial advisor and really know next to nothing about finance, but it is my vague impression that this would be terrible financial advice.