10 Gallon Paludarium build

OK, so I've got an idea for my paludarium. However, I need your expertise opinion on how to go about building it. This is my (very) crude drawing.

The brown denotes the land area, blue denotes water, dotted black denotes waterfall/stream, and dotted blue denotes an underground water(cave). This isn't quite my exact design, but it gives an idea.. I want areas underground for the fish to swim in, to give them more water/room. What's the cheapest, yet stable & safe way of doing this? I don't care much about aesthetics.

There's not going to be a background, just glass, but I'll make sure to add plenty of things to climb on, I just don't want to waste time on looks.

What's a good substrate to use for the plants on the land? & What is a good substrate divider?

How would you guys build this? I'm new to this, and am open to all of your advice.

I also want an above-tank sump, to keep my heater & filtering out of the tank. How would you guys build that? I want it above ground because I do not want to drill into the aquarium, so I want one pump that pumps it up to the sump, and let gravity bring it back down into the tank, where I "drew" the waterfall. How would you set up this sump? What's the best, but inexpensive filter media to use?

Thanks in advance for your help,
Cody

OK, I believe I'm going to make pillars of some sort, to hold up the land. But what should the land sit on? Egg crate is way too expensive. Any alternatives?

Can I use any type of plastic? Like sections of a milkcrate, and put landscaping fabric on it? Or plexiglass with drilled holes?