They lay eggs in moist dirt. I doubt they'll use gravel or rocks (of that is what that is) and it could pose a health risk if consumed. I use slightly damp coco fiber in a small tupperware and they seem to like it and always lay their eggs in it
Oh sorry didn't read under the picture that it was vermiculite and perlite. I'm not sure if its true but I've heard that vermiculite can cause skin burns. You'll want to get the female off sand as if she's laying eggs there's an increased risk she may eat it for extra calcium when laying eggs. You'll need to put the stuff in a tupperware or some other plastic box that retains humidity or it will dry out too quickly for it to be much good to the eggs. I like to use softer stuff like moss or cocofiber since they really like to dig and perlite seems rough and uncomfortable to dig through.
Yeah, that should be okay for now. Repticarpet works as a permanent substrate too, once you get rid of the sand you could use that unless you already had something in mind tile is also a good substrate.