When people say "cull" - it only means to remove from the flock. Kill, sell, give away... but remove from the flock. If you can sell pullets at point of lay for a good price, go for it! If you don't have that market, put them in the freezer. You are the only one who can decide what to do with...
Your chickens will probably all pile into the same nest box, no matter how many boxes you have. Kind of like ladies going to the bathroom - if one goes, more will follow. :)
I don't heat at all. But I have standard sized, winter hardy, small-combed chickens. I had a couple of large-combed roosters last winter, and they did get frostbite from the cold, but it was also -25 for a number of days when that happened. They were fine, by the way. Just had smaller combs come...
Before you plug it in, I want you to do this: When it gets below freezing, put on all your winter gear. From hat to boots and everything in between. Once you're all bundled up, go outside for a good while. Long enough to at least start feeling cool, but not cold. You'll know when you need to go...
Rarely to never. They get to go outside whenever they want to. And they don't need heat. When allowed to acclimate naturally, they grow down under their feathers and POOF! They have a nice down coat to wear all winter long, inside and outside. I will close the pop door when it's double digits...
I didn't vote, but you need to think about this - in the winter (You're in Maryland, correct?) your chickens will likely be spending a lot of time in the coop because they don't want to go out in the snow and cold. They will be bores, and possibly crowded. Winter tends to be when things go bad...
This ^. It's better to have more space than not enough, whether your chickens are seen as pets or livestock.
Something to consider would be an area fenced with electric wire or netting. Won't stop the hawks, but it could help with ground predators.
I'd make more room and keep them all. (Coming from the person who just ordered 28 chicks yesterday...) But if you are limited in space or resources to make more space, you are better off having a few and not crowding them. Behaviors from over crowding can get ugly real fast.