“If the pilot is flying over a crowd at the beach, that’s also a shaila, because I don’t know if the pilot is close enough to actually see individual people in their likeness.”
FAA regulations prohibit flying an airplane that close to people, except for takeoffs and landings.
As far as the Shabbos issue, banner towing is probably a good way to be self-employed, assuming you can find enough customers. But you can do your own advertising. 🙂
It could even be a way of doing kiruv. 🙂