Hi,
If your OB-GYN doctor feels that the combination procedures are safe for you, then it would be my recommendation that you do the combination procedure.
Unless you are very large or need a breast reduction, then breast and body surgery can all be done at the same time. I do not feel that an extra hour or so on your breasts combined with the tummy tuck and lipo would cause much of a difficulty. I understand that it sounds risky but you need to compare this to multiple anesthesia risks. These too can be argued are very small.
Case by case basis. If you are a smaller mom with a 1 1/2 hour tummy tuck and an hour breast surgery, why not. If you need more extensive body contouring and breast contouring, then perhaps break them up.
There is no question as far as cost that a combined surgery will save a significant amount of money but this should not be the primary reason for combining.