Some alternate locations in case you want to explore outside the usual midtown/lower manhattan spots:
-7 Train to Willets Pt/Shea Stadium in Queens-walk behind stadium into the "Iron Triangle". Several miles of junkyards, mechanic shops, and such. Roads aren't paved, it kinda looks like the set to Mad Max.
-E Train to to Jackson Heights/Roosevelt Ave in Queens-Has to be the most diverse neighborhood in NYC. Maybe the country. Every block is different-Pakistani to Colombian to Indian to Mexican to Philipino etc. Excellent place to street shoot and there's an elevated subway overhead so the light is great.
-A Train to 181st. A major shopping hub in Washington Heights (Manhattan). Tons of people along 181st buying from the stores and from street vendors. Not chain stores, but huge discount type places. Great spot to street shoot and people watch.
-2 or 3 train to 125th street, Harlem (Manhattan). Anywhere along 125th is good for street shooting. You can also walk N or S along any of the famed wide boulevards (Lenox, Frederick Douglas, Adam Clayton Powell).
-F train to Smith/9th. Not so many people around here but the neighborhoods of Gowanus/Carrol Gardens/Red Hook are all acessible by foot from this station. You can also head over to the Red Hook ballfields to watch soccer and eat at the famous food trucks serving Latin American food from many different countries. On weekends, the place is hopping.
Hope you have a great trip!