I plan on something similar, except I've never backpacked before and I plan on taking the subway to give myself a head start, then possibly a bus, before walking 15-20 miles to a campground (Croton Point Park) then maybe another 20 miles to Ward Pound Ridge Reservation. I'll do more research on the area I'll be walking through. All I know is it's not so good. Your hike is longer so you'd have a lot more research to do. I personally wouldn't take a chance doing it without researching the neighborhoods.

Google Maps has an option for walking directions, but it doesn't know which roads have sidewalks so you may want to zoom in on Google satellite map to look for sidewalks. I don't mind it for 20-40 miles but for something much longer I'd try finding a good route some other way.