Let me share my 2 cents with you. I haven't had PS, nor have I looked into getting a TT. However, from what I have gathered, insurance doesn't usually pay for an actual tummy tuck. They will usually pay for a pannilectomy (spelling?), which only includes removing that bottom hanging "apron" of skin. They don't always replace the belly button, tighten the ab muscles, or remove any skin toward the top of the stomach. Sometimes the doctor will let you pay the difference for a complete TT.
Sometimes they will give you a pannilectomy along with a hernia repair. It depends --I'd check with whoever is fixing your hernia about that.
I believe you need to have skin that hangs a certain amount past the pubic bone and have extensive documentation of skin issues that cannot be treated with medicines. So, check with your bariatric surgeon to see if he works with a PS, and start from there. They can tell you what is necessary -- you could also call your insurance company.
Also, check out the PS forum -- they will be able to help you. (Hope I helped a little)