Your coop is adequate. Everything we are telling you are just improvements that we feel are best. You know about prefab coops, and have already done much better for your flock!
The roof should be taller to keep the air from ventilation off their heads, and you didn’t mention roosts. Will they be miserable without roosts? Not necessarily, but if you can build that addition, a 2x4 laid flat about two feet up is probably best.
I am reminded about sand. Playground sand catches the poo, and you can rake/scoop it daily. It’s also a great dust bath year round!
The roof should be taller to keep the air from ventilation off their heads, and you didn’t mention roosts. Will they be miserable without roosts? Not necessarily, but if you can build that addition, a 2x4 laid flat about two feet up is probably best.
I am reminded about sand. Playground sand catches the poo, and you can rake/scoop it daily. It’s also a great dust bath year round!
I have 2 runs. I don't deep litter in the coop itself but my situation is very different; I'm sub~tropical. I deep litter in the coop run & with 12 birds in 2 months I have 3~4 inches of litter in the run. I clean the coop every other day. I am now throwing my litter into the 2nd run, which is much larger. If I were you I think I would bite the bullet & expand before you have winter issues when it sounds like you won't be able to fix problems.