A beauty, and indeed the rocks rock! For faster populating (and less memory use) it should be possible to use fake stones on the further areas, with an opacity mask by the same rocks through a default shader, and only populate on the fornt of the ring. But maybe that is more work than just populating.
For the stars you can also use a PF mask to let some shine on as bright as here, but dampen others by the greys and blacks of the PF, to get more depth/variety.