Here are some additional resources to improve the new York portion of your Masks of Nyarlathotep campaign.
Over on Mental Floss, there is an interesting article on pre-World War I apartment and their lavish floorplans (read the article here). Whilst it is unlikely that Jackson Elias himself would live in a place like this, perhaps one of the upper crusted leads could be found in a place like this. The Carlyle expedition danced in some seriously vaunted circles, after all.
Tell My Horse by Zora Neale Hurston is probably my favorite book on Voodoo practice. I for one love mixing up Voodoo with my Call of Cthulhu games.
Based on acclaimed author Zora Neale Hurston’s personal experiences in Haiti and Jamaica—where she participated as an initiate rather than just an observer during her visits in the 1930s—Tell My Horse is a fascinating firsthand account of the mysteries of Voodoo. An invaluable resource and remarkable guide to Voodoo practices, rituals, and beliefs, it is a travelogue into a dark, mystical world that offers a vividly authentic picture of ceremonies, customs, and superstitions.
Aside from Tell My Horse, I also think that Voodoo in Haiti by Alfred Metraux is worth checking out. It’s a bit dry but very informative (I wrote a paper on it in college) and the movie-inspiring The Serpent and the Rainbow is also a deep dive into the subject of Voodoo.
My party actually spent quite a bit of time trying to crack the JuJu House in Harlem. To be quite honest, they almost certainly spent more time there then it was worth. I believe the first player death came when one of the players attempted to use prestidigitation to conceal a theft in Harlem.
He was beaten to death in the street.
There’s an interesting article on Boing Boing today on Jazz in the roaring twenties. I’m sure a search of Spotify will reveal a great soundtrack for you to use.
I’ll leave you with a monstrously inaccurate but very great horror movie. White Zombie(1932), starring Bela Lugosi. Since Masks is more about pulp than history, I think it is perfectly appropriate.