This one is fine for any bike with a tire 25m or wider. It is fine on a hybrid or mtn bike, and you could tear it up on a cyclocross gravel grinder as the surface is crushed gravel.
There are no stores en route but you could venture across bridges to Bound Brook and Princeton if needed. Otherwise, carrry water and food. Lunch in Princeton, where you could end this ride, would make a fine day trip.
NJ Transit out of NY Penn Station to New Brunswick, there are no bike permits, it is not an issue. Return from Trenton, on the same line out, but 3 stops further than New Brunswick.
The East Coast Greenway coincides with the towpath as you near Trenton. If you stay on the towpath beyond the left turn onto North Montgomery, in a block or 2 on your right you will see a statue of George Washington high on a pedestal. The neighborhood is a bit run down but one day will surely be restored back to its colonial glory.
If you have a lot of time on your hands by the time you get to Trenton, you could continue on the towpath to Calhoun St, take a left and cross the bridge over the Delaware, pick up the towpath along the Delaware Canal going north, go to Washington's Crossing, cross that bridge and return back to Trenton on the D & R Canal towpath. There will be a few times that you will have to cross a bridge to contiune on the towpath as it will be on the other side of the canal. The path will be on one side or the other so don't despair. At Mulberry St, unmarked, just on the outskirts of Trenton, the path leaves the canal as you go south to pick it up in one block, just beyond the highway overpass. It now becomes paved asphalt. Trenton has social issues but I found users along sections in the inner city, which gave me a sense that the community deems it safe.
This route was originated by John Z.