As far as the coop:
You need wide perches (the wide side of a 2x4 or something similar)
LOTS of ventilation since that keeps the birds healthier and also lots of venting helps to reduce humidity and high humidity increases the risk of frostbite
I really like poop trays...
Remember that there are LOTS of coop fires due to heat lamps. I have had chickens down to -15ish with NO insulation as well as no heat, and they were fine (they weren't thrilled, but none died). People in colder places also manage with no heat.
As far as size:
You will get lots of answers to that question, some say that you need a tiny space so that the chickens can stay warmer. I go with as much space as possible since more space means happier chickens which means less egg eating, feather eating, each other eating
and such nasty behaviors. I have found that about 9 square feet of covered area per chicken is ideal. However, I get to that large number by having a warm insulated coop connected to a larger uninsulated shed (where a bunch of chickens sleep), and that is also connected to a greenhouse that the chickens get in the off season.
I also have a tiny bit of my chicken run covered with a roof, and I keep the feed and water outside in the run to force the chickens to move more.
Keeping the water outside is ideal since the coop is then cleaner and has lower humidity. Also, if you then use something to keep the water thawed it and cord are outside and less likely to cause a fire. I find the water stays thawed for longer if it is placed behind a wind block.
I manage to sell enough eggs to pay for feed, and I only have 21 hens. The key is to buy hens that lay super well. Nothing can beat a perl white leghorn for production. Mine layed almost every single day with ZERO heat as well as NO light, all winter long! No other breed that I have ever raised can do that. All other breeds need light to lay.
However, with that said, I prefer breeds with tiny combs, since that giant leghorn comb is prone to frostbite. I also hate breeds with feathers on their feet, since that hold icy mud and snow and increases the risk of frostbite on toes.
So, my favorite breeds are:
Dominiques, good egg layers, just enough meat so they are worth killing and eating, and cockerels are a good size and tasty, best personality, and beautiful pink-brown eggs.
Rose Comb Leghorns lay almost as well as the single comb production whites, but have a tiny comb!
EEs or Ameraucanas, or Olive Eggers since most have tiny combs, they are pretty, most lay well, and they have pretty egg colors.