I've read around here about sexing chams and I know about the spur on the back of the foot, I don't see one here but I just want to be sure from some of the veteran Cham owners.
I use a mix of both, with usually more soil, but other people use pure sand, or no sand at all, etc. So you have quite a bit of freedom, as long as the material, when moist, can hold up a tunnel.
I recommend making a few holes at the bottom with maybe some screen hotglued on so that any excess water can drain out if you mist a lot. Otherwise you don't notice but there are 2" of water at the bottom of the bin after several weeks. A few tiny holes drilled into the container solve that problem.
I've used that before with my veiled female, who liked it, but my panther female never took to Ecoearth very well. Just see how she reacts to it. But I love what you did with the fake floor! Clever.