I just put up my first box and I'm worried there is no perch inside. I just saw plans that had a perch inside. Is that necessary?
No need to worry! Some designs include inside perches so that older nestlings can look out of the box more easily, but these perches aren't necessary at all. Keep in mind that kestrels were nesting in any old cavity they could find for thousands of years before humans started putting up boxes, so a minor design variation like this certainly isn't going to be a deal-breaker.
Good luck! Be aware the majority of kestrel boxes go unused in the first year, but if that happens rest assured the lack of an inside perch isn't the problem. Good luck, and we hope your box has some tenants soon.