Paludarium Build

[GodFan]

Wasnt sure if this belonged here or not but I have alot od "general discussion" questions to go with this.
So this is a paludarium build. Plan on vampire crabs (I wanted frogs but I cannot risk the mold). In the water area I am not sure yet. I will list all my questions at the end. I want to do an "L" shape land mass with water in the open area. This will be in a 20 gallon tall aquarium. I plan to have one section built up pretty tall with a water fall flowing down the slope. I may also make a stream going through the "L". I will use pothos vine and different plants to add height. I plan on using gravel, rock, and pvc as necessary to build the land section.

So questions:
1) I ******CANNOT****** have any mold!!!! Somebody in my house is allergic so tips on mold control and prevention are appreciated! I am not using and wood or soil or anything above water to help avoid mold. Will this help?

2) What kind of pump will I need to pump water up about 12 inches for the waterfall? Preferably adjustable.

3) What fish will be compatable with the vampire crabs? I was considering cories but I dont know. Very open to suggestions. I may try bumble bee cats as well.

4) How do I work water heating? It would be akward to squeeze a heater into this tank.

5) Can I use slate from Lowes in the tank?

I am open to any and all other suggestions. I am including 2 horrendous sketches of my ideas
(First pic is top down second is face on)

Thanks and God bless!

 

[GodFan]

So I was thinking maybe I could make a false bottom for the land area and thus increase water volume, decrease the amount of rock I would need, and give me a place to hide the pump and heater. I could route water into this cavity through some strategically placed circulation holes. Using slate as a covering. I was also thinking I could make the stream 3-4 inches deep and pile seachem matrix on the bottom with rocks up top as my biofilter. Still have figured out my mechanical foltration.