It is really easy once you realize just how simple it is. It’s actually less work in the winter than during the summer when you are trying to keep them cooler.
The coop should not be air-tight, that would definitely lead to frostbite. The coop needs ventilation to carry the warm moist air up and out of the coop.
Consider practicing the Deep Litter Method. Simply layer the floor of your coop with pine shavings, and periodically rake the chicken waste into the bedding mix. Once a week, add a layer of fresh pine shavings to the top.
Collect your eggs frequently. A thick nest of straw in the nesting boxes is a great insulator.