How many hens? Looks like 3 nest boxes on the ground and 3 above that. Then 3 more way up above roost level. Likely your chickens will roost in the upper nests, they tend to go as high as they can get at night. 3 hens/nest is not a problem.
They DON'T "**** near freeze to death at below freezing and below 0 temps". My chickens' coop is a converted horse stall in a mid 1800's barn, 4' high plywood walls, wire above that on the sides and front. One side has clear plastic over it (well it was clear before all the dust stuck to it between the welded wire over all openings and the plastic). MOST of the chickens roost over next to the wall that doesn't have plastic. If it is -20F outside in January, it is -20F in the coop. I have never had frostbite on my chicken's combs, not even the Anconas with their big combs.
Yes there are different breeds and they can deal differently with temps. BUT 2 of my chickens are Cubalaya, as the name suggests, they originated in Cuba. The 2 Ancona are a Mediterranean breed. Neither have anything like Vermont winter temps. They behave the same as all the other hens in the winter. My girls hide from the midday sun in the Spring, Summer and Fall. For some reason they don't take their down coats off in warmer weather. Silly birds.
It isn't real deep litter if you clean it out (other than pulling some nice compost out for the garden).
DO NOT stuff the ventilation gap with straw in the winter!!! They NEED the ventilation.
I would move the nest boxes down. The chickens will sleep in them if they are up at roost level. And when chickens sleep, they poop. Nests that are low and not used for sleeping very rarely have any poop in them.
Along with the general conversation, I don't see any ventilation or light in the coop at all.
Definitely need 1/2" hardware cloth along the lower 2 or 3' to keep coons from reaching in and snagging a bird sleeping against the fence.
BIG coop?? I agree that my birds like light. If you put in windows, make sure they can open to let the heat out in the summer.
Because they have HUGE buildings where natural ventilation can't work.
At some point, yes too cold is too cold