I’m 5’2", 198 pounds pushing, 200 pounds. Do I have to lose weight before having a BBL procedure? If so, how much? (Photo)

Optimal candidates for surgery should have reached a healthy stable weight preferably with a BMI < 30. My recommendation is for pre-op weight loss. This will lower your overall surgical risk profile and likelihood of complications. 
With regards to your specific question, there is no quick fix. Cosmetic surgery is not a means for weight loss. Traditional diet and exercise are the first line. For those patients with a BMI of 35 (you are currently at BMI of 36) and associated comorbidites (diabetes, hypertension etc) you may qualify for insurance coverage of bariatric surgery (surgical weight loss).I would estimate a weight loss necessity of nearly 40 lbs (in order to dip below BMI of 30).
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

A good candidate has enough fat available for transfer in the procedure. The amount of fat that can be transferred in a BBL depends on how much fat the patient has to harvest and the amount of space there is to move the fat into. It is recommended for the patient to have a BMI of 30 or less. If you are too thin, a Brazilian Butt Lift may not be possible.

Plastic surgeons will have different opinions and comfort levels with regard to your BMI of 36.2 so it is best to ask the individual PS at your virtual or in-office consultation.  Other factors than BMI are considered in approving a patient for a BBL.  The two main reasons for targeting a BMI close to 30 is to minimize the risks of complications during and after surgery and to enhance results. Reaching a stable weight for six months prior to surgery is recommended.  If you are having difficulty in shedding the pounds, schedule an appointment with your PCP to discuss weight and exercise programs.  You do not want to spend the money for surgery and be disappointed with the results.