I'm new at this too and I went with an 8x8 coop and a 8x24 run attached for 25 birds. I know the coop is a little tight for the barred rocks and leghorns I have but our summers are awfully warm so I'm thinking any bird with half a brain, even half of a small bird brain, would likely stay out in the run most of the year. And, in a worse case scenario, if we're too tight on space we'll just eat a couple until we get to where we need to be. But I've heard all sorts of rules of thumb, and I'd think in NJ where winters can be pretty nippy your birds would probably sleep close so I'm guessing you could probably get by ok with even a small coop. I'd think if they need some space they'd just hang out in the run during the day because from everything I've read chickens aren't too bothered by the cold but the heat can cause problems.