So basically; always use Gloves Of Thievery no matter what, because regardless of how high your Sleight Of Hand is, you can still fail checks by rolling natural 1. Advantage = less chances of failing a pickpocket roll and better chances of reaching the high DC checks.
Again, just get a spellcaster who can concentrate on Enhance Ability: Dexterity (Cat's Grace) and suddenly any fixed bonus is better than another, redundant source of Advantage.
Since Enhance Ability is tier 2, and Bard, Cleric, Druid and Sorcerer can cast it, thats doable from very early on.
So no this is doable with level 3 characters already.
Of course what you otherwise really want is a Rogue with level 10 (guaranteed minimal roll 10, thus also no chance for Critical Failure), Sleight of Hand Expertise (+8 for level 9+), Dexterity 20 (+5), Guidance (+1d4) and Bardic Inspiration (+1d10), and really any other item that can push the skill.
And in the end you always have Player: Reload to fix mishaps of course.
