Couple thoughts here:
1: That is a very cute coop. Now you need to make it appropriate for your situation.... ie: cold weather chickening.
2: You are going to need insulation. Seriously. I'd do it on the ceiling too.
3: Ventilation needs to have some cross breeze or ways to make the air move. You've gotten some good suggestions here for this already. Wondering: do your windows open from the top down? I like to keep the tops of my double hung windows open in the summer for ventilation. Looks like they are across from your large vent. This would work for summertime.
4: I saw someone else recommend putting in some vents at the gables. This is what I would do regardless of whatever else you do. Reason is because that large vent is directly across from their roost and you won't be able to use it in the wintertime. It will blow WAY too much cold air on the chooks. The ventilation needs to be up high. Get out your jig saw and cut 2 holes in each gable (4 holes total 8 or 10 inches MINIMUM - not 3 inch circles) and screw vents over the top to the exterior side. Then on the inside, attach the cut out pieces to a hinge/hook & eye so that they can be flipped up and hooked when weather gets bad. This fix should cost you no more than $40-50 and will make a world of difference inside the coop. Believe me, my DH was ready to KILL ME when I told him we were going to have to cut holes in his beautiful coop (as per Pats instructions), but we HAD to and it made a huge difference.
5: If you have no way to get electricity to the coop, then how are you planning on keeping the water thawed this winter? Electricity for the coop will unfortunately be a necessity in Wisconsin. You'll likely need to provide at least temporary heat when the going gets tough (remember -27F last winter??) if not 24/7 (which is what I do) and have a way to hook up a heated water dish to keep the water fluid. It might be necessary to rethink the location of your coop. Do you have any space that would work that is under some large trees, providing shade and natural cooling?
I'm in MN and am happy to help you hash out some ideas if you need help. Just PM me.