1. Not that tough of a project if you have access to a welder or someone that does. If you stick with the stock E-body rear, you'll have to move the spring perches 1" inward on each side. The only tricky part about that is setting the pinion angle correctly. You could also get a '65-'70 B body rear, it bolts right in with a 1" relocation kit.
2. If you stick with the E-body rear end, you'll want around 6" of backspacing to center the rim. But, that will depend on how wide of a rim you use.
3. This will really depend on your taste. I run Summit Legend 5's, 17x9", with 5" of backspacing all around. But I run the narrower B body rear, so I don't need as much backspacing to center the rims. I only run 275 wide rear tires, with the 1" offset kit I have seen up to a 315 wide tire back there. That would need a 10" wide rim, which can be done with the offset kit.
4. Dr. Diff.
http://www.doctordiff.com/ He sells the only true 1" offset kit, which allows the use of the B body rear. The mopar performance offset kit is only about 3/4" offset.
5. No, not if you use a Dr. Diff kit. The mopar performance kit requires shorter springs, it was designed for super stock springs.
If you really want to figure out what will fit as far as rims/tires, check out the tire combo thread. Especially toward the end of the thread, there's a lot of combo's posted with offset kits and wide tires.
http://www.cuda-challenger.com/cc/index.php?topic=19470.0
