I agree on adding more windows if possible (don't know if habitat for humanity or other architectural salvage/recycle type stores are open nowadays, that's a good way to get 'em cheap) and then covering them with hardware cloth so you can safely open them for additional ventilation. Some additional natural light is super nice to have in a coop.
We don't have buffalo gnats around here, but if you do you might want to go ahead and use screen mesh. I have heard terrible things about those gnats.