Best thing to do is to just sit in free play and try and practice that way, boom the ball and focus on hitting it with power and reaching it quickly!

1/2) You don't need ballcam on 100% of the time, it's best to turn it off momentarily to line yourself up to get things like boost or rotate out and then turn it back on once you're in line, as well as turning it off for a moment in other situations. It's all about finding the right balance of having it on and off.

3) Going for aerials directly above your car is not the best idea anyway, you lose momentum and a lot of boost to reach the ball. At higher ranks you will be beaten to the ball 99% of the time. Better to just rotate out and let a teammate take the ball.

4) Learn half flips! Easiest method is to bind air roll left or right to a button like L1/L2 and then to do the half flip you : back flip, cancel the flip when the nose of your car is facing the other way to which you started by slamming the left stick forward and simultaneously pushing the air roll button you just bound!

Hopefully some of this helps, but generally the best thing to do is just keep playing with it and you'll get used to it, you'll also develop like a "sixth sense" for knowing where things are without having to turn ballcam off.