First of all, I agree, I'd worry about fixing up your floor. Cut out all the bad spots and weld new steel in. SEAL THE EDGES with a quality "Seam-Sealer" (before painting) wherever you make a patch, it will save the repair for many years over not sealing it. You can get good seam-sealer at your local auto parts store. It's not cheap, but it's worth it.
As far as the seatbelts, the rear seatbelts are attached to the Frame of the Rear Seat, not directly to the floor. Do you mean the seat frame is rotted itself where the belts are attached? If so, if it is really bad, you may want to just get another seat in good shape, it's sometimes not worth trying to patch something like that.
You won't need a 1" body lift for 33s, a 4" suspension lift will do very nicely, and, yes, I would recommend the Skyjacker kit (check with Quadratec, they have a totally complete kit for around $600 roughly). I had great luck with a 2.5" Skyjacker kit for 8 years before passing it on in a partial trade a few months ago, when I parted my old Jeep out. The new "owner" of the kit loves it! You're gonna probably get some posts from others that it is junk, etc., and to buy all these other heavy duty kits. That may be fine if you off-road all the time, hard core, and rock crawl, but if you don't, you may find the other kits a bit of overkill and rough-riding. The Skyjacker gives a super-smooth ride, my 2.5" kit rode much better than stock. <img border="0" title="" alt="[Wink]" src="wink.gif" />
Good Luck with the "project"!