@Bionaraq one of the problems that I have seen people trying to drop is they want to immediately put their foot in the rear toe plate. This upsets their balance and down they go. I have them drop the ski and actually keep their barefoot off to the side of the single ski for a while and you will easily keep your balance and can gradually transfer to the slalom. Most of your weight will stay on the ski, but the foot out to the side just helps balance. Also, there is really not a need to stuff it into the toe plate, and you can just put it on top the toe plate with toes in front or behind it, and if you feel like you are losing your balance, just put that barefoot out to the side and you will see how it immediately balances you out. Once you feel totally in control, then stuff the toes in the RTP.
I would also stress that the posture should be good and handle kept low at waist level with arms straight.
And on the slalom start, I think I qualify as a bigger guy, having skied at 285 and currently 260, the key is to push your toes on the front foot down so you don't have a 90 degree bend in your front ankle. A wider ski will push a bigger wall of water if you do not get the tip held down in this position. A firm rolling down of the throttle is better than just dropping the hammer. Too little is not good either, as you will not get lift and will run out of air!
Good luck with your addiction..