I admit I have not read every page of replies, but I would like to share one thing that has proven to be incredibly useful in winter where I live. In winter, they days are short, so short that when I take care of the chickens in the morning before work it is generally dark, and often when I return at the end of the day, it is dark again

. I have a small solar powered motion sensored light that I hang on a nail on the outside of the coop (I do not have electric to my coop). When I get close, the light comes on. I can see what I'm doing when I take care of the chickens! I don't need an extra hand for a flashlight, nor do I need to remember my headlamp from the house. The light is always there waiting for me and I'd be lost without it. Additionally, since I hang it on a single nail, I can take it down and hold it in hand like a flashlight if needed and shine it inside the coop to check on the girls or shine it anywhere else light may be needed.
I read many pages of debates over heated bowls. Personally I found it just as easy to use a rubber bowl and knock out the ice and refill twice a day. I caution you that heaters can fail (happened to me) eventually and you should still check on the birds at least once in the morning and once in the evening so if by chance your heater failed you can get them fresh water before it's too late.
I do not insulate, I do not heat the coop, it is below freezing most nights of the year, and for several months most days too. I selected cold hardy breeds and gave them a wind proof coop and a wind block outside.
To the OP for your coop, I would take a piece of plywood and close off one side of that space underneath the coop. Choose the side the wind generally comes from. This will make a nice wind block for you and give your chickens a very sheltered place to hang out in bad weather. My girls love it. I leave it year-round because it makes shade for them in the summer too!