I bought it and easy to use and for windy area like Mountain House Ca its very useful for plants and tree support .
Yes, the birdhouse should fit on the pole if you put a small landing on it so the birdhouse can sit on a sturdy platform.
Use a step ladder and a sledgehammer they go right in
Fence Post Driver https://www.homedepot.com/p/205960880
I didn't see untreated posts at HD, but these are likely only dipped or soaked as they have no pressure treated marks.
They are 8' long and about 2" in diameter.