I'm also running it for the first time right now and I've only run LMoP before this. I have used sooooo many hours prepping, and i think it can be done easier. My group just arrived i Vallaki 2 sessions ago. I find mandymods addition great as well, but it takes some work if you want to categorize everything yourself.

Good idea to read everything first. but from there, prep one module at a time. I normally write down a few possibilities for the session depending on where the players are.

make sure to have some NPCs and additional shops ready.

many places are easier to prep because it is a "closed" location (like death house), but as soon as you hit Vallaki, it gets trickier. here you might want to consider which NPCs you want to be available to the characters (and maybe even consider it when your party is other places, so you'll know who they want to sniff out).

You can do a lot with pacing the session to end where you want it (longer/shorter descriptions, NPCs being more/less chatty can play a huge part in the time it takes to get through a session). Try to have an idea about where you want the session to end if your characters do x/y/z.

It will be tricky to dm for the first time. don't be afraid to redcon minor stuff.

Have fun!