About the AI:
What should your enemy do and not do and when and when not?
About update purchase etcetera:
Do you want a menu in which this is done or does the player upgrade his gun when walking over, should the player be able to switch guns at all times or just at certain places/times in the game?
How and when does the player gain experience and how do you want this displayed, what does experience mean for the gameplay and how do you want this implemented?
About Weapons equip coding:
Instance variable weapon
if player chooses handgun
set variable weapon to handgun
- if player variable is handgun
trigger once
set group handgun to active
in the group handgun have all the events that are diiferent from when the player has another weapon.
About character:
Either create animations for all you want or have the hands head pinned to the player sprite..
Another option would be to use an external program like Brashmonkey's Spriter to animate the player from loose parts and insert the whole in Construct2