I shouldn't count on getting more hens as a solution. Roosters tend to have their favorites and that is who they will mate with most.
To give the hens with the worst feather loss a break you could confine them to a run for a week or two and still have your rooster out protecting the flock as...
A nail file is just fine. You only need to file off and sharp edges and round off his toe nails.
Is Shaggy a different breed to your hens?
If he's a young rooster he may learn to mount the hens causing less damage as he matures. Bare backs look terrible but as long as there are no open wounds...