Yes you could put a window in the door, maybe beside the pop door, or over the nest boxes, lots of possibilities. Plexiglass can be cut, and self made windows can be any size you need.
Ventilation is a more the better thing, just don't want the girls getting in a cold winter draft. Yours look high enough to keep the girls safe. Vents can be covered many ways if you are in colder climates and need to close some down too. Not sure where you are, I'm in Maine and my vents stay open almost completely all year