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
_{(source: threadbombing.com)}

See Here

In general: You chose which AC to use

The answer to your question is very straight forward:

If you have multiple features that give you different ways to calculate your AC, you choose which one to use. (PHB)

Monk/Druid - Can use either

For Monks specifically there is an official ruling by Jeremy Crawford:

The druid/monk could use Unarmored Defense or the beast's AC calculation.

Barbarian/Druid - Can use either

Barbarian unarmored defense is worded exactly the same as the monk's so the previous ruling is applicable here as well.

Draconic Resilience - Beast's AC except, maybe, if the beast has scales

You can't use features that the beast form doesn't have

Per the PHB

can use them if the new form is physically capable of doing so

and Jeremy Crawford

Wild Shape: keep your racial traits, unless told otherwise or they require external features (wings/hands/etc.) the new form lacks.

You cannot use any racial features that your beast form does not have.

Draconic resilience depends on specific physical features

The Draconic Resilience feature says:

parts of your skin are covered by a thin sheen of dragon-like scales. When you aren’t wearing armor, your AC equals 13 + your Dexterity modifier. (PHB)

Note that this effect is predicated on the presence of dragon-like scales on your skin specifically. This means that this feature requires those to be present.

If you wild shape into a beast with skin and fur, the best thus lacks the necessary physical traits to make use of the draconic resilience.

Very similar official ruling

Jeremy Crawford made a ruling about a lizardfolk's natural armor feature. The description of which is:

You have tough, scaly skin. When you aren't wearing armor, your AC is 13 + your Dexterity modifier. (VGtM)

Note how it is very similar to the description of draconic resilience.

His ruling was:

The lizardfolk's Natural Armor specifies anatomy: tough, scaly skin. It doesn't apply if you're wearing a beast's skin in Wild Shape.

However, if the beast has scales it might qualify (DM's choice)

Note that in the above ruling Jeremy Crawford specifically says "wearing a beast's skin". It is possible that if the beast has scales (for example the crocodile or ankylosaurus) that it might qualify as now having the necessary physical feature (scales) thus allowing you to use draconic resilience.

This will likely come down to a DM call as to whether any of the creatures on the list have a "thin sheen of dragon-like scales", but it seems like a reasonable ruling to allow.

Stone Sorcerers - Should be able to use either (if the beast has skin)

Per the discussion above about draconic resilience, if you turn into a beast that has skin you should be able to chose between the Stone’s Durability or the beast's AC.

Note: Stone Sorcerer is UA material so it is non-final.