Greyhawk Thieves Guild
D&D 5e. Interested? Definitely! Able? Possibly, not even probably. Based on your success rate for just getting a game going, I'd be excited to try. I probably can't do much worse. Though if I do I hope it leaves you no worse than you are now.
I prefer greyhawk over any other prefab world. I played Living Greyhawk in 3.5 and much of the lore is saturated into the system regardless of the edition. I know the least about Greyhawk, the jewel, itself, and more about elsewhere in Oerth, such as Dyvers, Bandit Kingdoms, and Shieldlands. I would be not only willing, but excited to read up on the changes, and differences in 5e. I love the criminal theme (?) for 5e, and would really like to see your thief have it. If not your thief, then maybe another major player.
My idea would be an arms race against the lawful entities as well as misery noble caravans. There would likely be big scores, a few being stings set up by the guard or merchants, but many legitimate but risky marks. Most would be staple thefts though, or those where you'd have ample "outs" planned out as Larry Lawton puts it. I'd probably want to assemble a list of, oh, maybe ten NPCs both protagonists (rather on your side) and antagonists. Some would be mooks, some major players, most that do as their told but without true conviction. In fact, if you'd prefer I can even make rival thieves's guild, or one where your party could try to join and take over from the inside. We can have the Tu Pac thieves code, to robin hood's "rich do not keep their earn, for nor vice versa" to "I covet what the system has denoted I may never have" all the way down to "I enjoy the fact you take solace in the guard protecting your wealth. All the better that I may pick your paltry locks"
I'm thinking of a "death" of a party member being rather like the British capture of the best locksmith and giving him a free release if he could pick the "unpickable"
lock. So while merchants' guards may strike to kill, guards would strike to capture. This would also create impromptu prison breaks, which could be fun. The idea would be fail forward, and should you all get captured, worst case scenario, you'd meet some shady person in the joint who may want help for the "Great Escape".
I have the above the idea, and I'm excited! For the mere fact IRL my "religion" being the practice of sedition. I've had both RL and fictional depiction of crime sliced thick and thin and I have confidence (other than RL interference) that I can GM a game pulpy or gritty, or somewhere in between. I would highly prefer the game be mature, but would be negotiable on either other category if the players and circumstances warrant that discussion.