Coop looks good, I love overbuilt stuff haha!
I setup my coop with 6 nesting boxes for 14 hens (3 in coop, 3 in run) - they randomly choose the one they'll lay in, but have definitely been using all of them. I did 3 across a 48" wide dimension, so each box is roughly 15"x15" footprint inside, about 16" tall - they have just enough room to get in and turn around.
My floor/walls are OSB painted with like 5 coats of semigloss paint that I had laying around. I was going to use 1/8" thick plastic wall sheeting (after getting inspired by Carolina Coops' HDPE interiors), but the cost was too high. I also considered buying elastomeric roof paint, but decided to just use what I had as it was better than our old coop and I can always paint/add materials later down the road. Old coop is bare OSB floor/walls and deep bedding - after 20+ years the OSB is still in great condition and not rotted; I'd guess without deep bedding it may have rotted due to funk soaking directly into the wood instead of bedding.