How much (or little) information do you need to tell your story? I have a hard time reaching a stopping point, and when I do, I often get the urge to start changing things again.
Its fine to do world building for its own sake, if you enjoy it. But if you intend to use your world for anything, then it’s not so much “when is it enough” as “what is it for”. It’s fun to develop, say, a tavern full of interesting characters. But are the players going to go there?
My suggestion would be to develop the rough sketches of the world at large, and then focus more on the players’ surroundings, and do a bit between sessions as you anticipate what the players are interested in pursuing. Even if you let them go where they want, they probably aren’t going to go anywhere.
Also, if you let the players develop the rough sketches of where they want to go during a session (“I want to find a rowdy tavern in the seedy part of town!” / “My character is a veteran, maybe he has an army buddy living around here!”) their prompts will help you improvise, and they’ll be more invested as well. That will do for the first session that the place/character appears, and if it feels like something that’ll reoccur, you can build upon it between sessions to make it come alive more for subsequent sessions.
Others have given very reasonable answers, but “do enough, and then do as much as you want for fun” is probably the answer my heart desired most to hear, privately.
This is a pretty good bit of advice, especially for those working with a tabletop gaming group. “Build a bit to get started” -> “Play a bit to get the feel of your group” -> “Build more based on what they seem to enjoy / want” is a solid bit of advice, albeit one that makes you wait a bit to start showing off your worldbuilding chops.
It doesn’t have to take that long, because by focusing on the things the players are (probably) going to interact with, chances are much higher they’ll actually experience all the detail you’ve added. And if they want to venture further afield, asking them for prompts is a good way to make sure the world you develop keeps being relevant.
I’m a big fan of how FATE does campaign development, and would recommend reading the relevant sections 1, 2 in the SRD, even if you’re running a game in a different system.
I’ll definitely take a look at that. I’m not familiar with FATE, but I am working on some homebrew stuff now, so it sounds useful.
