The rim of the basket is 3.05 metres off the ground. The size of the backboard is approx 1.8 metres by 1.1 metres: it may be varied. As a result, its height off the ground is not strictly regulated.
If the ball bounces off the backboard or rim and you catch it before it hits the ground it counts as a rebound.
no it is encouraged
hit off backboard
You can hit a shot off of the backboard and into the hoop, but you can't hit a shot off of air into the hoop. You can easily shoot more accurately with the backboard.
No, it is not considered out of bounds if the ball hits the side of the backboard. Unless it bounces off the side of the backboard and then out of bounds before you or someone else can catch it.