I've completed the Nocturnal Quest and returned to the Thieves Guild. I've been trying to minimize self-spoilers, but I do know that there are quests to rebuild the guild and become the official guild leader. I've been doing dozens of the ambient tasks that Vex and Devlin give, assuming you had to do a certain number to trigger the next major quest. Do I just need to keep doing this, or is something stuck? After about 15 of these random quests I started having my suspicions.

i am doing the same with the jarl of riften. i want to buy the house in riften (honeyside?) but i just keep getting little task to do with no option of house buying?
i just finished blindsided quest and havent returned to the flaggon. ill let you know what happens when i get there.
what was the last thing you did for the guild?

You have to do about 5 quests in each city, except for Riften, so 20ish in total.
Once you've done the special quest for the city in question, cancel future quests for that and focus on the other towns.

Like Fleapants said, but just be sure to make sure the "restore" Thieve guild quests don't sneak up on your quest journal. I had finished the first one, did a TON of misc extra Delvin/Vex quests, got flabagasted that I done so many, checked my quest journal, and voila, I had had another "restore" quest there the whole time, one I'm fairly sure Delvin didn't actually talk to me about.