CUTE!!!!! I could use your painting energy around here!
I definitely second the "wired" suggestion for the holes. And if you need to leave the lid up for ventilation at night, I would find a way to have that be wired, too. And of course the door ... you want the birds safe and secure while they're sleeping as they are blind in the dark and defenseless little kittens while asleep.
OR ... the whole setup could be in a secure run. How small any openings can be, and how deep under ground you should secure and what kind of security you need from above ... all of that depends on the predators in your area.
I myself have spent a fortune on hardware cloth. Sigh.