Do you let your chickens free range on severe cold winter days, or close them off?
Mine close to never free range... too many predators.
Mine do have access to a fenced run. If the wind is blowing they do not like to enter the run.
Because of that i have a large shed that connects to the coop, where i put the feed and water.
the pop door to the fenced/secure run does stay open.
I was thinking about porting a door into a attached greenhouse, from the coop to allow them a exercise yard in the winter
mine get the greenhouse in the winter. Mine love it. You do need a huge door (human size) from the greenhouse to the coop/run/shed/connection otherwise there will not be enough ventilation in the greenhouse. My greenhouse has a few eves that can be unblocked in the winter for better ventilation in addition to the large door.
I keep ready about frostbite at these temps, but I don't remember our chickens back in PA getting special winter treatment.
Frostbite is more of an issue if your humidity is high, or the perches are skinny, or they get their feet wet.
Also, wet snow can clump on feathered feet.
I have cold and high humidity (I am right on the coast)
For me the single combs with those tiny upright points will freeze off. No way to stop it (unless the chicken lives in the house with you... )
But, as long as you keep the feet healthy, a little frostbite is OK, and will take care of itself. No doctoring is needed.
Also, are there any particular breeds that are more hardy for these regions?
With my cold + humidity I have breeds with clean feet (feathered feet are a huge problem with humid snow or icy mud), tiny to zero wattles, and tiny combs.
Don't be tricked by things like "Icelandic chickens" being marketed for cold climates. Many of those have single combs (which will frostbite). If you research them, historically Icelandic Chickens were kept in the house or warm large animal barn all winter. They were not out in the cold.
I did find that Leghorns aren't actually as bad as you would think, because their huge comb folds over onto the face. However, they all have pretty large wattles.
Small single combs always frostbite at my place.
I really like Dominiques, Ameraucana, most EEs (as long as the combs are pea combs), Wyandottes, d'uccle, and Spitzhauben.