Looks about 24 to 30 inches long by 12 or so inches wide so maybe 3 or 4. Depending on what the floor is made of. Also the gap by the handles needs closing.
Technically yes. I don't know how to grow meal worms but know the birds would eat them. Problem might be ensuring enough worms survive without being eaten
Looks like you have the healing process taken care of. Can a predator get to your quail? If so get then secured. Think when you put what have done to clean the wound you pretty much have taken all the steps readers would suggest.
I use a converted rabbit hutch. Enclosed all four sides with plywood, installed a light at one end on the lift up roof of hutch. Once feathered out I removed one panel of wood to let natural light in.