Where I live, it rarely gets below 32 all year long. From what I have read about it, combs do not get frostbite unless it gets much colder or there is too much moisture in the coop.
Do not leave water in the coop and make sure there is good ventilation.
Yes, good ventilation and with no drafts. If it gets really cold our hens will huddle in one of our spacious nestboxes (16x16 inches by 2 feet tall). We once found 4 hens in one box!