It is certainly a very big surgery you have planned.
The question of combined surgeries comes up frequently. Experienced surgeons have a feel for how quickly they can do a case, the health of the patient, the unique risks the patient has, and the overall scope of the operation. As Dr. Rand points out, there are special "red flag" areas in combined surgery (such as implant/mastopexy, liposuction plus full TT, etc) where an experienced plastic surgeon will exert extra caution.
There are easy breast lifts and there are difficult lifts, the same for tummy tucks, liposuction, etc.
The health of the patient also factors in. There are young healthy patients in whom the risk would be low, and heavyset sedentary older patients with medical issues where the surgery would be unthinkable.
A seasoned board certified plastic surgeon with decades of experience will guide you through the risk analysis.
As always with plastic surgery, if you have doubts, do not proceed.
It is my philosophy with combined procedures first to make conservative choices. If during surgery after the first procedure the patient is 100%, the operation proceeds to the next procedure. If the patient is 99%, the operation is over and we return another day.