Actually, the rolling was usually done on the rear wheelwell. The rear tires are usually larger and this was where it was needed. Plus, the steering linkage would want to turn the wheel if you tried it up front. The rear wheelwell is usually made up of multiple layers of metal spot welded together, whereas the fronts are usually single layer. A dolly and hammer were usually used up front because of this and it's also easier to get at.
Just like anything else, depends on your touch. Some guys have been able to do it without chipping the paint, it depends on how much roll you want. Obviously it's best to do before final body work and paint, but after rust has been taken care of.