1) Rough it up with a red scuff pad.
2) Use high-build primer, 3 coats.
3) 300 grit wet sand the primer for a flat surface.
4) VHT high temp would be best, here.
For rear swaybar: absolutely yes. It does not need to be fully removed from the car, but you need to disconnect everything such that you can back out the bolts and lower the subframe ~1.5" for the appropriate clearance.
Great fix, OP! Used the same technique on one of my other cars with a Solo Performance exhaust. Had polyurethane hangers that were a bit slippery and just couldn't get the tips to hang centered. One worm gear clamp on each side was just right to keep the exhaust from going cockeyed.