Great thread, many good suggestions.
When working with any "thin metals" the biggest issue will be returning the original shape without further stretching the metal. The previous advice of working the area slow and steady, taking only "small corrections" at a time is very important. After it has been over worked, over thinned, stretched, it's had to put the Genie back into the bottle. They make hard nylon hammers for hammering metal that will help prevent stretching and marring. Every time you hit the inside of the fender with a common "ball peen" hammer you are creating a small, stretched circle that will add to your problems. It's much easier to fix a dent, than it is to correct a "previous owners" screwed up attempt.
I have a bead roller with the factory supplied crank. I can see why you would want to change to a large wheel instead of a crank for power. It gives you greater control and the handle is never "out of position", the circular wheel is always in your sweet spot.
John