Ideal candidates are at a stable weight, in good health , and have excess fat in some parts of the body and too little in other regions. Gaining weight before the procedure is to no advantage and when you lose weight again the fat cells will shrink just like the donor site fat cells. ...
You should wait at least 2 weeks before sitting without a support cushion and sleeping on your back. Sitting with no support too soon can harm the newly moved fat cells.
Its good that you have a vision of what you want. It simply needs to be communicated to your plastic surgeon. Bring examples of what you think looks good to your consultation, and be available for digital imaging of pics of you so you can get a good sense of the proposed direction of change...