looks good. I tried something like this years ago for some mantellas. Have you run the waterfall yet? Make sure that no water leaves the pond, even a little splash can saturate your substrate. Also with a small body of water you may have to top off quite frequently.
I now just use leca and let the water go through the whole tank rather than try to contain it. Much simpler and I'm so glad I don't have to deal with soil anymore.