You can also buy the book for about $20 with the rules for making custom playbooks. I'd definitely start with the standards though.
There is also A Horror Borealis, an 80s-set AP from the people who made the Cryptid Keeper podcast. I haven't listened to much as I am awash in APs I want to listen through but you can find it at https://player.fm/series/a-horror-borealis
I usually use https://tabletopaudio.com/ for games I'm running. There's so many ambiances there, you can likely find something that works for you. You can also build your own ambiance with the soundpad. Plus, being able to tell Alexa to play Dwarven City to all the speakers in the house makes for some amazing immersion.
Have you ever read the Time Lincoln comic? A number of history's biggest names are secretly an organization of time-traveling heroes led by Abraham Lincoln, fighting the good fight against the BBEG, Void Stalin. I'm afraid there's not a good website to pull information off of, but the series is on Comixology, and is worth the read. But time traveling Stalin organizing a team of history's other despots was the first thing that jumped to mind reading your post.