Thank you for your question. As long as you are healthy, do not smoke, and not too far from your ideal body weight you should do well. Trying to minimize the amount of time you spend laying on your back for the first two weeks after surgery will help to minimize resorption of the transferred fat. Ideally if you could lay on your sides after surgery, it would be helpful. This is best done by propping a pillow under your back while in bed. This is a tall order when you have had both procedures, but do your best. Good luck!
In my opinion and experience, combining an abdominoplasty with fat transfers to the buttock is a great idea. When performing an abdominoplasty, we routinely use liposuction to thin the overlying fat layer. This allows better definition than a tummy tuck alone in patients who need it. Rather than discard this fat, it can be used to augment other areas of the body, such as the buttock. You may have a bit more discomfort than the tummy tuck alone, but this should be nominal and not require any additional time off of work.