What is involved if obese and get a Tummy Tuck for muscle separation?

Thank you for the question. 
Generally speaking, it is always best to achieve long-term stable weight prior to proceeding with body contouring surgery. Doing so, will increase the safety of the operation, will likely improve the outcome of the operation (best chance to achieve an optimal aesthetic outcome), and will decrease chances that additional surgery will become necessary subsequently. 

In my practice, I do not ask specific patients to achieve a specific weight prior to proceeding with tummy tuck surgery. I simply ask patients to achieve a long-term stable weight where he/she feels comfortable and does not expect significant fluctuation postoperatively. 

Having said that, there are a subset of patients who  are above the ideal long-term stable weight who benefit from panniculectomy surgery. The panniculectomy operation involves excision of the lower abdominal wall pannus or overhanging skin/adipose tissue. It is not considered an  aesthetically driven procedure;  it is often performed to help with concerns such as skin breakdown, infections/rashes… 
 
The vast majority of patients who have had children and/or weight gain/loss benefit from muscle plication during tummy tuck surgery. Muscle laxity is usually easy easily determined with physical examination prior to surgery. The separation is also easily visualized during surgery.

When the time is right, seeking consultation with well experienced board-certified plastic surgeons will  be your next/best step.  Best wishes.

For safety reasons, you should lose weight and get your BMI below 30 before surgery. Good science shows you have a much higher complication rate at this weight or above. Also, for cosmetic reasons, you should lose weight and get your BMI below 30. You will NEVER get a flat belly at a BMI over 30 because at this weight you still have fat deposits inside of your belly that aren't touched with a tummy tuck. In the end you will have had all this increased risk surgery and still end up with a round belly.