I have a few opinions that you can take or leave. After having birds for a bit over 30 years and several coops, I've change the way I do things. Chickens for the rookie are a lot like kids for a newbie. By that I mean, the first kid gets high end diapers, top grade food, walkers, strollers, and every thing known to man. By the time the second kid comes around he's getting pop tarts and a kid leash if he's lucky.
First, don't overthink this. It's a chicken. The coops needs to feature several key elements with the first being protection from predators, the second protection from wind, third, dry and rain proof to a reasonable degree. Everything else is way down on the list and you do what you want. I discourage the use of "external" access to next boxes. First, it's a second point of failure for predators but more importantly it allows you to do things without being in the coop. You need to be in the coop….daily. If the reasons aren't obvious, I'll expand on that.
I have 40 birds and their coop is 15x10 or so. I have no idea if it meets the new age parenting "size requirements" but I don't particularly care. The birds are free ranging meaning the coop is where they stay at night only.
You need to figure out what your goals are and build accordingly. No matter what, DO NOT OVERTHINK THIS.
The single most beneficial item I have ever used with mine is a self closing door. It opens at daybreak and closes at sunset. I have lost many birds in the narrow timeframe between sundown and "whenever the hell I get out there"…it's a life saver. Literally.
The second smartest thing is double walled hardware cloth on windows and vents. Do it. Don't get cheap here.
I'd probably also abandon the idea that you are going to move it or take it with you if you move. Build it right. Build it strong. Build another one if you move. If you want it skid it, you certainly can. Just head to your local shed building supplier and see how that is done and copy it.
For your roosts, make them flat and 2x4. Wide flat roosts are easier on the birds feet. It's easier for them to roost and more importantly it allows them to settle on top of the feet having both the bottom and top protected from freezing and cold temps by board or body.
No other heating is needed. Make sure your coop is wind and rain proof and they will be fine. The birds you are getting locally were bred for New England. They will survive no problem here.