Yes. The GPL license covers the add-on's code, not what you create with it. Your models, renders and games are yours to use and sell.

Lower Viewport Resolution (Surface Damage) or Viewport Cut Resolution and Iterations (Fracture). Renders still use the higher render settings, so the final quality is not affected.

Yes. Every button works on all selected meshes. Copy to Selected gives other objects the same damage, each with its own variation or as an identical copy, and New Variation rerolls the pattern on all of them.

Turn on Use Damage Material in the Surface Damage modifier to give the damaged areas their own material. Fracture has an Interior Material for the faces inside the cracks. Procedural or box-projected materials work best there.

Yes. Click Apply Damage to make it permanent, then export as usual. For soft, game-ready edges on fractured objects, put a Bevel modifier before the Fracture and keep the Weighted Normal after it.

Real geometry. The damage is cut into the mesh, so it works in any render engine and can be exported. Faces the damage doesn't reach keep their original topology.

It works on any mesh object, but closed (watertight) meshes give the best results. Open surfaces, like a single plane, are ignored. Close the holes or add a Solidify modifier before the damage.