Closing their door,after making sure you have all of them is for their safety. It is another barrier that predators need to breech. Stoney has excellent luck with his birds roosting in trees!! (HI Stoney!) , but others have not. If you have an open heated dog bowl for a waterer in your coop it may prove to create to much humidity. Too much humidity is more of an issue to chickens than temperature.
I also sprout oats for Greens in the winter. Most people do not. Alot of things work, but I do agree with Stoney,,,,don;t baby your chickens!!!!
OH!! and welcome to the friendliest thread on BYC!!!