Chickens, for the most part, can handle cold winter temps. Chickens produce tremendous moisture through respiration and poop...and also ammonia. Good ventilation is a must no matter what time of year. If you don't have enough ventilation in the winter, you run the risk of the chickens getting...
Great job. I would suggest you enclose the utility closet with wood or everything you store in it will have a coating of white dust from the chickens. (My girls have been in their coop for 4 weeks now, and all the flat surfaces must have a 16th of an inch of white dust.) If you don't mind it...