BBW mother of 8, looking to do full mommy makeover, arm and thigh lift (photo)

Thank you for the question. Generally speaking, combination surgical procedures are done routinely. However, you are wise in being concerned about the safety of combination surgery; risks/possible complications do increase with increased length of surgery… 
In my opinion, the combination procedures you are considering would be too much to perform in  a single session. As you likely know, achieving a long-term stable weight, prior to proceeding with elective surgery would be ideal when it comes to safety as well as outcome  considerations. Generally speaking, the “ideal” patient for mommy makeover surgery is one who has completed pregnancies, is psycho socially/emotionally/financially stable, has an excellent social support system surrounding him/her, is capable of arranging enough recovery time, does not smoke and who has reached a long-term stable weight.It is best to evaluate each patient's suitability for combination surgery on an individualized basis. During this consultation process, after a complete history and physical, the SAFETY of combining these surgical procedures becomes of paramount importance. Plastic surgeon, anesthesia provider, duration of surgery, surgery facility all important considerations.
Your best bet: choose your plastic surgeon very carefully; everything else including good judgment/advice/planning, anesthesia provider and safe surgery facility will follow.  Always keep priorities (safety,  avoidance of complications, and quality of outcome) in mind as you make your decisions.  Best wishes.

helloHave in mind that being over weight increase the risk of complications during and after your surgery, the BMI range is 30 and it is important have a stable weight in order to have any surgical process. 
I recommend you maintain your weight in a healthy range and then consider the surgery, you will achieve amazing results.
Also you can make an appointment with a board plastic surgeon for a good evaluation and to talk about your goals and options.
Good luck.-