Sounds like a pain to clean and sanitize TBH. Especially the sand and water feature.
I tried using the sand with my beardies and omg it was a NIGHTMARE. Urates and sand make this God awful cement that adheres to everything. If you want something other than traditional substrate - have you looked into creating a viv with bioactive substrate? A nice little isopod colony for janitorial duty might be right up your alley.
Be careful about what kind of water fall you use. Many of them are difficult to clean every nook and crannie of (inside the hoses especially) become breeding grounds for bacteria - exactly what you are trying to avoid. A simple water bowl is easy to remove from the cage and spray down with a disinfectant covering the entire surface area. If your heart is set and you do want moving water you might want to look into the water fountains for dogs and cats. They are much much easier to sanitize.
Sounds like you'll have a cool set up though
