A charecter good with guns needs high endurance, perseption and strenth.
For the Tag get guns, medicine, barter.
And for the first few levels upgrade them. after level 5-8 start going with sneak, repair, science, lockpick and speech.
Agility is the special abilites associated with guns 10 agility would give an extra 10 to guns plus if you tag it thats another 15 so you could start with around 40 guns.