A. Some species may produce 3, 4 or even 5 broods, so be sure to monitor the nest box for an extended period before cleaning the box, or wait until the following spring. Some birds may use the nest box in the winter as a retreat from the cold.
If you feel like painting, be sure to paint only the outside...never the inside! No lead paint. Easy colors, not too dark and not too light. Natural wood with a good stain is always a safe bet.
Make sure your birdhouses have good ventilation and drainage.