That they are & OP, what I did is pretty much what you describe. I have 12 x 24’ for two horses. I think the only difference is that the entire end is open (no doors), so escape is easier. I would definitely recommend removable dividers for feeding – they come in handy for so many other things. Mine is a super sophisticated leftover piece of fence tape hung from bucket straps, haha, but it works fine. I agree with other that flexibility is awesome & my experience has been, the more modular things, the better.
Horses can definitely trap each other anywhere - even with my wide open shed & friendly geldings, the submissive one can find himself doing some contortoinist leaping to escape boss teeth & has skinned himself on a wall a couple times. Some of that is just sensitive young horse dramatics, LOL, boss is not generally overly violent & gives warning looks first, but nonetheless the submissive ones don’t always do the best job of planning ahead. And mine are two horses that will also often graze off the same clump of grass, so it’s not like they are enemies.
I can understand why you want a back wall since you live in MN (brave souls) – I would recommend making exit doors wider than a standard dutch door if you do that for escape reasons, to save hips. I don’t think I’ve ever heard anyone say they wish their doors were narrower, so I can’t think of any downsides to doing that offhand (other than non-standard door sizes, but if you are building your own or built on site by contractor, it shouldn’t be a huge price difference).