Welcome. I must admit, I had to look up squab. I do not have pigeon or bunny experience, but can speak about chickens. I like the coop size you are giving 6-hens. With chickens, space takes care of many issues. The 6-chickens need 2-3 nesting boxes, but will all want to lay in the same one
. Chickens need coop ventilation above where they roost. I cut holes in my building and then cover the holes securely with 1/2 hardware cloth attached with screws with fender washers. For predator protection outside, 1/2 hardware cloth with a ground apron (hardware cloth walls, attach to bottom, then run along the ground 18-inches and cover with earth or stones). This will prevent digging predator from getting in your run.
