Hello Paul, and welcome to BYC!

Glad you joined.
The rough numbers:
4 sq ft floor space, 1 linear foot roost space, and as close to 1 sq ft of PERMANENTLY open ventilation per bird plus 1 nest box per 4-5 hens in the coop.
15 sq ft of space in the run if they aren't free ranging or enclosed in a large pen.
Walk-in is always better.
Poop boards are the stuff of gods.
Keep roosts 1 ft away from the walls and each other horizontally to minimize poop splatter on the walls and bombing chickens roosted nearby. I can be hard to get poop out of feathers.
Chickens are viscous little raptors particularly at roost time so if all the roosts are at the same level, there is one less thing to fight over.
Lots of windows that hinge top and are backed with 1/2" hardware cloth so they can be suspended open during rain without worry of water infiltration into the coop.
There should be no opening greater than 1/2" anywhere in the secured coop when locked down. All ventilation needs to be secured with 1/2" hardware cloth too.