We had alot of chickens untill health issues for my son and my wife slowly dried up their numbers. What we figured out was that they don't lay real well when there is not enough light in the day. I installed a light on a timer to turn on and off a couple times a day, morning and night, to give them more light hours. It worked like a charm. The production was almost as good as the rest of the year. Having more chickens in the coop works well for keeping them warm. Safety in numbers
Chickens have photon sensors in their brains. To get the most eggs, you need 14 hours of daylight...it mimics Spring Time when they lay the most. You can run the lights 24 hours per day, but then they just think it is summer, and they cut back on the number of eggs.
As for chickens getting cold, their combs tend to get frost bit. Roosters are the worst because they have the larger combs over the hens. To combat this, when it is real cold and you fear frost bite, just take some bag balm on your fingers and run over their combs. It prevents frost bite, though they are no worse for wear if they get a little nip in their combs. We always have a tub of Bag Balm around anyway, it keeps all kinds of problems at bay. Like pecking issues, they don't like the taste of it, so they won't peck one another after they get a taste of it. And for ducks that are fighting, slather their necks with it and the aggressive duck cannot get a purchase on the other one, and after a bit they will stop fighting.