I've got four hens. Two are too old to lay and one is too young, but the fourth one hasn't slowed down at all. I'm in Middle Tennessee, and my layer hasn't skipped a single day. I work from home, so getting the daily egg in a timely manner isn't usually a problem. The hens are in a rather small coop without a run, so I make sure they get about half an hour a couple of times per day to free-range in the yard, and that seems to keep them pretty happy. We've also started giving them plenty of dried mealworms so they've got extra energy to stay warm.
For the coop temperature, I went to Home Depot and had them cut two pieces of plywood. One is leaned on the side of the coop and one is leaned against the back. This keeps the winter wind from ripping through there and causing a draft, and it keeps the coop a few degrees warmer than it otherwise would be. We also increased the amount of cedar bedding in the coop to help keep them a bit warmer. If the temperature is supposed to be near freezing at night, we close the nesting area after they bed down to preserve their body heat.
My newest bird isn't ready to start laying quite yet, but she's helping out and getting some practice. She's a feral bird that I recently added to the coop and the other three don't like her very much, so she spends most of the day upstairs in the nesting area. After my layer lays and goes back downstairs, the new feral bird nests on the layer's egg to keep it warm. My laying hen does me a solid and has started crowing immediately after she lays, so I've got a natural alarm to know when to go grab the egg. (I pretend that she's crowing to alert me of the egg, but she's probably just ****** that the feral one is sitting on it. She stops squawking as soon as I get the egg.)
On extremely cold days, I've brought the whole flock indoors in a dog crate for a couple of hours so they can warm up.
Hope some of this advice is useful, especially the part about leaning plywood against two sides of the coop. My flock spends a big chunk of the day huddled up in the back corner where the plywood blocks the wind and allows them to preserve a few more degrees of heat.
Peace, eggs, and chicken legs.