Check out the Togglers by Hilti. I buy them by the box of 100 but maybe you can find them or something similar at a hardware store. The advantage of Togglers over Mollys is that the screw can be removed without the fixture falling behind the wall. I use them to mount grab bars in bathrooms. The disadvantage is that the wall has to be at least 1/4 inch thick.
The holes can be filled with something called Patch and Prime. A mesh patch is put across the hole and the spackle covers it up. No priming needed. Just paint over it.
Maybe just a visit to an Ace hardware store would give you more ideas.
