You might look through the "coop designs" section of this forum for some more ideas. But I do understand seeing one in person makes it easier to visualize.
https://www.backyardchickens.com/coopdesigns.html
It might help on the comments a bit if we had an idea what your climate is like. But no matter where you are, you need ventilation year-around.
I use a 5" or 6" board across the front of my nest boxes for the same reasons Crabella mentioned.
Some of those external nest box covers look like they will leak. You can overcome the potential problems, but external nest boxes sometimes cause leaks, are sometimes weak points that allow predators entry, can allow drafts, and can be a problem in extreme weather. If they are on the sunny side they can get really hot in the summer or if you truly have a cold climate, the eggs can possibly freeze in the winter. I built internal nest boxes and put an external door so I could check them without going in the coop, and I never use them. I find it is much better to go inside the coop to see what is going on. I've found an injured chicken, a possum and a couple of times, an egg eating snake. There can be legitimate reasons for the external access, such as people gathering the eggs that a rooster might attack, but I find them not worth the extra hardware I bought and the extra complexity in construction. On that one, does the external nest box cover have a secure lock to keep predators out?
I notice a roost at the same elevation as the ventilation. In a hot climate or the summer, that is not a big deal, but in the winter if you are in a cold climate, you do not want drafts blowing on the chickens when they roost. The primary ventilation should be over their heads. I have a window at the same height as the roost for summer use, but I also have permanent ventilation all around the top of my coop under the overhang. Any cross breezes in the winter is well above their heads.
The theory behind putting a 2x4 flat instead of on edge as a roost is that, in really cold weather, a chicken will squat on the wider board and cover its feet to prevent frostbite. I use tree limbs instead of 2x4's. Some parts of my tree limbs are smaller than the narrow side of the 2x4 and some are thicker. They sleep all over, location being more important to mine than thickness of the roost. My outside temperatures rarely get much below zero Fahrenheit, and I have not had a problem with frostbitten feet. But you can lay it flat if you want. In either case, round off the corners so their feet can more comfortably grip and so you can remove the splinters if you use 2x4's as roosts.
That's not a bad idea for a pop door if you can keep it from jamming when you raise or lower it. You can probably overcome it by rounding the corners and having it kind of loose in the runners, but I'd think just having one rope on the middle might subject it to jamming. I also like a lock on it, or something that would prevent a raccoon from just putting her claws under it and lifting it. Having an internal siding door with a nice lip on the outside at the bottom will help, but it would not take much for a raccoon to get a paw under that one with the shallow lip.
It's hard to tell. Do all windows have hardware cloth over the opening to prevent predators when the window is open?
Probably enough for now. Hope that helps.
