Hi AvB.
I am also learning and quite frankly, still have a long way to go, but if I can give you my 2 cents worth, this is what I have found useful to avoid catapulting...
First off , as someone else mentioned, uphaul seems to be very important to get a good control of the sail. It will respond better. Those numbers on the sail are actually useful.
The boom height and the mast position should be adjusted so that you can have a good stance when using the straps, not too forward hopefully, so you can use your body weight and lean back comfortably.
Secondly, and that, not too many people told me about... pay attention to the water; look at the direction of the waves, look for gusts or V shaped patches over the water, that can indicate a change in direction. When I see one, I usually try (before hitting it) to steer towards the wider end of the V, this way my board is in a better position to jump into it. And just before you hit it, try and slow down just a bit and get a good grip on the boom, get ready to lean back as it pulls you in.
Before I learned how to read the wind on the water surface, I used to get catapulted a lot, not knowing what had just happened.
BTW I ride some old gears, I just recently upgraded to a 1992 85 litre board, so I can't say how much a newer board would help, but I am getting better at it.
I also never sailed the mouth of the river at GB. I got stuck there once and got washed by the current. I usually sail between the sand banks. I usually take it to weyba lake or N shore rd (twin water) as it is closer to where I live.
I started recording my trips using the windrace app with my phone. You should try it. I haven't uploaded any here yet but it is useful to get to know a particular spot and check out your record speeds (I'm at 37.6kts atm

)
Anywho enjoy. I hope my tips helped.