Lovely flock!!
You may want to turn your 2x4 roosts so that the larger side is the part the flock will roost on. This will help on those -0F weeks, the larger side allows the flock to literally sleep with their feathers covering their feet so that they don't get frostbite. I also insulated my coop, but it will still get cold in the coop especially if we have a worse winter than last year (the corn tassels are very high this year, and and old wives tales states that the height of the tassels is how much snow we will get that winter).