RE: why not ask the pros?
- center of gravity low == hard to get catapulted
- center of gravity low == easier to get into back straps (cause YOU are in control)
- commit 110% to your lines, your arms won't help you much
- smaller fin works well too
- mast further forward helps
- keep an eye on that windward rail, don't let it get more than level
- I wouldn't put the boom too low (I never go under shoulder height)
since you can already waterstart you should consider getting into the straps before planing (in overpowered condiditons), you already have a feeling for hanging low from the sail
Its all about control, lack of it -> catapult
Control is when you are in charge == low center of gravity (no sail is going to pull you over).
I know when you try it its a bit scary, but do give it an honest hour or two. You will end up flying faster than before in stronger winds with larger than expected gear.
And as stated before never underestimate the advantage of loads of downforce generated by low center of gravity.
(a few days ago I also had a lovely 18-22kts session on an ST137 with an 8.7 3cam free race sail in up to man high mushy waves weighing ~ 86 Kg. Most of the others gave up with smaller boards and sails (who started out with me when wind wasn't up yet). In those conditions you can still do a bit of blasting and carve through your gybes. This has something to do with technique and will. If you don't have the will to learn the technique you won't get there).
one more thing: over powered ==
- floatation vest