Your coop seems very nicely climate-appropriate to me. The sleeping in nestboxes is undoubtedly b/c they are so high compared to the roosts.
I don't think you oughta enclose it with anything solid (if you actually have *problems* in winter, you can certainly do something *then* with plywood if needed, but I kinda doubt that would happen) but you should realize that if you leave it totally open to the World Of Raccoons like that, eventually sooner or later you ARE going to lose chickens at night. (Or to possums). There is nothing there that would even mildly slow 'em down (certainly not the privacy fence). If that's worth it for you to not have to deal with closing them in and letting them out, that's fine; if you would rather protect them at night, that's fine too; it's a personal decision. All I'm saying is, sooner or later (and there is NO way of knowing when) raccoons will find the dark-and-white-meat buffet. And of course once they've had a sample, they tend to keep coming back, even if you then *do* try to erect greater defenses.
Good luck, have fun, nice setup you got there and I bet they are happy chickens,
Pat
