Hi Payton,

Basically your describing most of the vivariums out there with a water feature.
Whites love to soak and a nice water area is always cool.
My whites would have it trashed in a night since they poop in the water and love to drag in as much substrate as they can,

I'll just toss some random thoughts at you since you can create a great viv with some pre-planning and a good knowledge of how your plan will be serviceable in the future.

I think you would need to determine where the water for the waterfall is going to be fed from. A false bottom using egg-crate would probably be easier for changing water and adding makeup water as the water evaporates.

You can separate a water area by using plastic dividers and silicone in place to seal off a section for water and then having a stone or clay bottom in the non water feeding area.

Your pump needs to also be accessible in case of problems later in the vivs life.

I would look at some vivs that have water features in members photo albums and over some searches on the web for some ideas as to a how to add in and separate your water feature.