Do you think it's possible to achieve this? The gas giant mod allows you to spawn asteroids inside it, but i'm not sure if thats just because there are no voxel surfaces on it.

Asteroids cannot spawn very close to the surface of a planet/moon. This mod can only remove asteroids, not add more.

I'm trying to get roids to spawn next to a moon's surface, but no matter 0 or 1 on the max gravity settings they wont spawn within 20km of the surface

New asteroids will not appear if they are loaded while in any gravity well (even an RSS proxy), but it will not unload existing asteroids that have already appeared. If you modify an asteroid by changing its voxels, then it will continue to exist no matter what. So if you want to build on an asteroid in proxy space, make sure that you mine at least one voxel to make the asteroid permanent.

Same question as @Quartofel. Since you wrote both, I would guess yes; but it's also hard to see how they could be made to be compatible ...

Will it remove asteroids if they come into contact with gravity well from a Real Solar System mod moving planet?