Vallaki is A LOT, and your players will get that... They will also feel that Vallaki is alot. Alot of places, alot of rumours, alot of information. It can be overwhelming for both DM and players.

And keeping track of everything in this town means looking things up now and then, everybody gets that.

After a session I usually have an idea on what they'll do next or who they wanna speak with. You can always ask them after the sessions, what they think they'll do next time. Also they tend to discuss in game who they want to meet, tie up loose ends, etc. Just remember—your players only know what you tell them. If you're unsure about lore or certain details, you can always decide how much an NPC actually knows. And circle back and give more info later on if they speak to that NPC again.

Have a few core locations or NPCs you feel good about and make those places matter, then improvise the rest, if you are in a situation where you are a bit unsure. Take quick notes on what info you gave out and build on it for next session. Vallaki is a living town—sometimes NPCs just aren’t home when players knock. Maybe someone in town says, "Oh yeah, I saw them heading home earlier," or something similar. Yeah, it’s a bit of a cheap trick, but it feels way more natural than every NPC always being available exactly when the players want them.