One of the great things of New York is how different the character of the city is not just from one borough to the next, or even one neighborhood from the next, but even one block from the next.
You should also take the very real byzantine and aging subway and tunnel systems and build cool subterrainean locations and groups.
Some material that might inspire subterranean adventure set in NYC:
* John Saul's
The Manhattan Hunt Club (
https://www.amazon.com/Manhattan-Hunt-Club-John-Saul/dp/0449006522).
* The film
Dark Days, Marc Singer's documentary on the community living "Freedum Tunnel" an abandoned section of the New York subway.
* Caleb Carr's
The Alienist, while set in 1895, at the time Teddy Roosevelt was Chief of Police for NYC, you can take some of the encounters and locations and update them for modern times.
* Since Vampires are a major party of your story, read up on the Vampire Club sub-culture of the Goth sub-culture in New York (e.g. the Long Black Veil club, The Court of Lazarus). This is just to help you google for pictures and interviews and essays that can help you create locations and encounters. I think you are better going with existing fantasy works for Vampire organizations, rather than the Pax Vampyri and the Black Trinity (
http://www.courtoflazarus.org/main.php?module=paxvampyri) or the Temple of Set's Order of the Vampyre. The former is basically cosplay with codes and the second takes itself seriously as a religion.
* Central Park is a great place to build encounters. It is big, over 840 acres. A village of working-class african americans (Senaca Village) was violently cleared out to create it, which has been the basis of ghost stories. Ramble Cave is an interesting feature of Central park that is no longer accessible. Starting the in early 1900s, it was a frequent area of crime, suicide, and harassment of women and was long ago closed down as too dangers to maintain. But it is still there. Maybe that's not the whole story? What dark secrets are hidden in Ramble Cave? McGowan's Pass is the ruins of the Academy of Mount St. Vincent, which closed in the 1850s. Its driveways and foundtions are now used as a mulching and compositing area, but you could come up with something more interesting. Cleopatra's Needles. An obelisk in Central Park and the oldest monument in NYC. It is 3,500 years old and was taken from the Egyption city of Iwnw (a/k/a On a/k/a Heliopolis). Its twin now stands on Victoria Embankment on the River Thames in London. Too much to go into here but the Freemasons, based on items found under this monument when the Romans moved it in 12 BC demonstrate link between Freemasonry and ancient Egypt. There are all kinds of conspiracy theories about this obelisk and two others in NYC and how they line up. You could build an entire adventure around the obelisks of NYC.
* Read up on the various NYC ghost tours, they may give you some story fodder and interesting locations you might not have thought of.
One nice think about NYC is that their is just so much interesting history and locations and subcultures to draw from.
See the Secrets of New York videos from NYC media:
http://www1.nyc.gov/site/media/shows/secrets-of-new-york.page
The Atlas Obscura Guide to Hidden New York has some good pictures with short write ups that can inspire many and encounter location
Recreating the old "speakeasy" feel has become a trend and these hidden bars make for good locations to meet NPCs:
https://www.thrillist.com/drink/new-york/secret-nyc-bar-speakeasy-hidden
Too much fun. Love NYC.