Err, i meant to say through the riften thief guild quest chain.

Would points in stealth tree bee needed?

just points in pickpocketing. you dont need stealth at all. just wait till theyre looking the other way.

Having points in pickpocketing does help but the perks is where pickpocketing shines.

Sure each points reduces chance of successful pickpocketing but the first perk you gain a 20% bonus. So make sure if you want to start pickpocketing riften have enough skill points to place into perks.

Also if you haven't notice when you highlight an item when pickpocketing there should be a % on the bottom of the screen somewhere that tells your chances of pickpocketing that item, note: 90% is the highest chance you can get.

Seriously, with max sneak and all perks pickpocket success seems to be no better than 75%. Just quicksave before trying.