I don't know why you should get a thief for your pickpocketing???
Why don't you take bard instead cause a bard has a good lore, can use any weapon, can wear chainmail ( with penalties), can cast spells, and pick some pockets. So when you create a new party make sure you have both a thief and a bard.
My party is:
All human.
Ranger.
Fighter.
bard.
thief.
cleric.
mage.