Whether or not it's a requirement varies by surgeon, but most of them will tell you that getting to your ideal weight and in relatively good shape will optimize your results and make your recovery easier. The hard cut off I've seen from many surgeons is a BMI of 28. Most recommend a BMI of 25 for good results.
With metoidioplasty, it's very important to have good body composition as any kind of fat may obscure the penis and/or make it impossible for you to use it to stand and pee, have sex, etc. They are able to do a procedure called a mons resection that can help reduce the amount of mons fat, and many people end up having this done just because that region is hard to lose fat from. But they can only remove so much fat at a time. So for an overweight person to have optimal results, it may require more than one mons resection (which will be seen by insurance as a cosmetic procedure, so you'd be paying out of pocket at least for that procedure).
Depending on the form of scrotoplasty that's done too, having thicker thighs may cause issues with testicular implants. This would be a consideration for both meta and phallo.
With phallo, the bigger you are the fewer choices you have in terms of donor site. And the more subcutaneous fat there is in the donor site, the thicker the penis will be post-op. It can be reduced down in size after the fact, but similar to the mons resection they can only take a certain percentage of the girth away per procedure. I want to say it's something like 10-20%. So if you're very big, that may mean multiple extra stages to de-girth the phallus. And I think they'd want those to be complete prior to doing any kind of erectile device implantation. So it could likely add 6 months to a year to your total surgical timeline.
If you're in the US, Crane and Chen would likely be willing to work with you. I am not sure about Dr. Berli at OHSU. Dr. Schechter won't schedule surgery unless your BMI is under 28 or your body fat percentage is acceptable to him. Dr. Bluebond-Langner I'm not 100% sure on. I had already lost weight by the time I consulted with her. Dr. Salgado might be willing. I have seen him work on heavier guys.
Have you consulted with a personal trainer and/or a nutritionist? Even with a health condition, I'm sure a professional would be able to find a diet and activity plan that would help you see some improvements.
