Have had my abdomen cut open: twice.
As for incision, I can grab & pinch at the side of the waist side to exclude internal organs, then cut there. Or would it be easier to use as fat guy, and bury it in the abdominal fat?
Cut the explosives into small enough portions to fit the hole, and push a lot in, followed by the wireless detonator. It will be enough.
Pain is largely in your head. It's easy to train people to endure lots of it; women are best at this. Add a local anesthetic, bleach her hair, give her a bit of pot to mellow out and the chick will pass for an American.
Decompression is not a problem. There's no reason to wait to blow up the plane -- doing it at low altitude insures a greater body count.