Should I seperate my mommy makeover surgery into two separate surgeries?

There is no right or wrong answer for this.  I commonly do breast lift and tummy tuck in the same procedure. Perhaps the plastic surgeon that you chose has a particular reason why he is recommending you separate them. I would direct your concerns to him and only move forward when you feel completely comfortable with your decision.  Best of luck!

Assuming you are in good health, I see no reason why an extended tummy tuck and breast lift could not be accomplished in a reasonable time frame in one session. Longer surgeries do have a higher risk of complications, but this is a common combination and could be done in about 5 hours.