I have Ameraucana's and bantams, they tolerate the same type temps, don't know where you are, but we are in Maine. I have 5 in a 4x8 coop and have not had any issues. I would suggest wrapping plastic up to roof, allowing for roof and eves to be ventilation in itself.
Using deep litter method will help "compost" and insulate the floor from the cold. As long as you toss in some corn, feeding a slightly higher fat for energy and a perch that allows them to cover their middle toes (longest toe) then you will not have to worry about any problems.
Personally I do not want heated water, lights etc in winter due to the frequent power outages we endure. If you do not get them accustomed to warmth, they will be prepared for everything nature offers.
Some folks let their girls out in winter, I never do. Don't let them get started and on horrible january days when the themo doesn't budge off 0 if we're lucky they aren't going to be diving for the door. If you do want to let them out, plastic in their run, put shavings down to keep them off the cold.
Good luck and I change the water 2 times a day and give a cup or two of hot water and mash for breakfast. It gets more liquid in them and a lot like hot oatmeal in morning, warms you up. I feel it helps them in egg laying, warming not needing as much energy to heat up when they can put it into laying.
Purely old fashioned suggestions and not that of many of our friends, so good luck and I'm sure your girls will be fine!