I would not use the corner mirror brackets that use screws or nails to hold them and the mirror. Geese will bill at the, and could start working them loose and eat them. Adhesive is a better option, wood frame around the outside if you want a second level of securing since uninsulated none...
No feed or water in the night houses here. However if you don't provide a secure nighttime house they are open to predators to kill them. Always best to secure them at night to keep the, safe. A fenced yard is not going to stop raccoons, wondering dogs, cyotes, bobcats or mountain lions.