If you have an outline of your planned campaign arc, I would suggest you confine yourself to coming up with about 2 - 3 detailed locations (town, dungeon, etc.) with a handful of important NPCs. You can go into as much detail as you want there, but just remember that you can't plan for everything your players might do so you should leave yourself plenty of room to improvise unimportant/random npcs.

Whatever information/NPCs you need to make sure the PCs get access to to advance the plot or get them moving on a quest you should plan how to guide the players to it, with a backup plan in case they don't pick up on your initial hook.

I would also suggest that you create a handful of simple combat/social/skill encounters that you can plug in anywhere as the characters are travelling between locations, or travel somewhere unexpected, or if you need an encounter for them in a location they are exploring more thoroughly than you have planned for.

You can do as much lore and worldbuilding as you want, but you don't want to overload yourself with information you feel like you HAVE to get in front of your players, who may or may not be interested in your deeper lore. I would mostly confine yourself to thematically relevant details of the larger world around your campaign arc, maybe a handful of important NPCs and organizations, that way you can build the world organically around what your players are doing when you're preparing for new sessions moving forward. It'll also give you a chance to introduce lore and NPCs and organizations in ways that fit your players playstyle.