From what I've read, allow about 12in on the roost per chicken, and get them as high as you can with one or two where they can choose their height, hopes this helps as I'm still learning..
As cold as NJ is I would recommend a 2 x 4 board turned flat ways so that your chicken's feet can be better nestled in their downy under belly at night. The flat (wide) side of a 2 X 4 is 3 1/2 inches.