I just set up (okay, I set it up around November) a very similar vivarium (10 gallon) to what you guys are contemplating. It's really not that hard, and doesn't cost that much. If you are planning on having a waterfall, using a simple 70 gph fountain pump or better will allow you to circulate the water, and that in and of itself should allow for adequate filtration (after all, you are letting gravity act as your action system for an "undergravel" type action).
I would recommend using a false bottom that is sloped toward the front. I'll post pics when I get home. I used coconut husk chips as the substrate, and used a little pea gravel in the stream bed at the front . . . but you can't see anything now that the Java Moss has covered it all (and that didn't take long at all). With a 10 gallon, you are a little limited on the number and types of plants you can use, but I have a small maidenhair fern (the leucs love it), a pothos cutting (which will probably become a nuisance before long), an earth star, and some tiny Drosera sp. to go along with the Java. There's also a little coco hut and a small piece of driftwood in there, besides the flat rocks which form the waterfall.
Seriously, I bought the pump from Quality Captives for something like $10, I already had the egg crate, screen, planting media, etc. So, other than making the top from some scrap glass, plexi, and screen (which is a little frankensteined at the moment), this setup only cost about $20 to setup, as I used mostly plants from cuttings from my other setups.
This will be a fun project. You'll love it, and then you'll be hooked. Of course, it's probably going to cost you guys a bit more unless you have some of this stuff just laying around. Let me know if you have any questions. I'm such an enabler when it comes to getting into darts . . . they're just too great not to enjoy.
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Homer W. Faucett III, esq.
Purveyor of Trivialities and Fine Nonsense