What others have said is correct: you need to do it with lots of boat speed and be careful not to get too high after the gybe. You asked about mainsheet and traveller: traveller should be centered and the mainsheet tight. Aside from being where you want them anyway, having the sail centered means that the boom goes across more gently.

In terms of avoiding capsize, don't worry too much about the kite. The most important thing is for your crew to get their weight across at the right time.

Paul