Stress levels from confinement rise the closer you pack them in, which reduces things like egg production and feed conversion as well as making them tetchy. Just think about people on subways, airplanes, elevators...then imagine being in that situation for 18 hours at a time in winter! Plus...
I'll be setting the posts for my coop this week...it's going to be 8x16" and I'm going to frame it in such a way that I can add onto it later as well. Four square feet per bird is actually the recommended amount...but you can squeak by on less with such a large run.
Since you're in Mass. and prone to the kind of winter weather that would keep chickens in their coops for potentially extended periods of time, I would build the coop to maximize the amount of space per bird to minimize problems like pecking. I don't think many people have ever regretted going...
If you do your run completely out of HC (which makes sense to me), just make sure it is adequately supported with your posts.
I am building a 8x16' raised coop and am going to attach a hoop-style run using cattle panels overlaid with HC and a wooden base. I'm still considering whether or not...
Well, the openings in the fencing are wide enough to allow weasels and such in, as well as raccoon paws. You may want to wrap with hardware cloth as well.