As a "healing witch," the Healing hex is absolutely worth it. One free healing spell for anyone every day. You will use this all the time instead of wasting potions/money. You will use this hex forever.

Be very aware that Cackle requires a move action, and can very quickly degrade your action economy until you are caught in a move-and-cackle trap.

Don't worry about the Fly skill until 5th level.

Against anything mindless or immune to mind-affecting effects, your hexes are all but useless.

Prehensile Hair is extremely useful for touch spells or trip attacks.

The Spite spell + Vampiric Touch is a fantastic combination, doing a minimum of 3d6 points of damage to a successful attacker, and granting you that as temporary HP.

Do everything in your power to get a Witching Gown.

Only effects requiring attack rolls yield critical hits

The splash damage of an alchemist's bomb isn't increased on a critical hit because the alchemist didn't make an attack roll to hit the splashed creatures with the splash damage. The rules for Critical Hits say

When you make an attack roll and get a natural 20 (the d20 shows 20), you hit regardless of your target's Armor Class, and you have scored a "threat," meaning the hit might be a critical hit (or "crit"). To find out if it's a critical hit, you immediately make an attempt to "confirm" the critical hit—another attack roll with all the same modifiers as the attack roll you just made. If the confirmation roll also results in a hit against the target's AC, your original hit is a critical hit. (The critical roll just needs to hit to give you a crit, it doesn't need to come up 20 again.) If the confirmation roll is a miss, then your hit is just a regular hit.

A critical hit means that you roll your damage more than once, with all your usual bonuses, and add the rolls together. Unless otherwise specified, the threat range for a critical hit on an attack roll is 20, and the multiplier is ×2.

Emphasis mine. The rules for when a creature takes the action Throw Splash Weapon include

A hit deals direct hit damage to the target, and splash damage to all creatures within 5 feet of the target.

The alchemist made an attack roll to hit directly the target; the alchemist didn't make an attack roll to hit the creatures within 5 ft. of the target. Thus even on a critical hit the alchemist deals his normal splash damage (although he still deals extra damage to the target hit directly).