There are so many options that work, and most all can be done for well under $400.00. I have several types of set-ups and think I prefer the ones with false bottoms and falls/waterways. There are a lot of web sites devoted to building a false bottom. In any event, you will need a drainage system, the most simple being a gravel bottom to which I add activated charcoal, although this may not last long, separated from the substrate by someting like garden weed liner and siphoned out from one corner manually with an aquarium air hose whenever the water builds up.
The last few I've built have been false bottoms supported with "egg crate" or similar material on pillars of pvc, cut about 2 inches shy all on sides. I then purchased a plastic food-keeper dish for the pool portion that holds smooth rocks, which contains the waterfall pump and tubing to the top of the falls. This is set into a cutout portion of the egg crate. These are punctured around the sides (a heated ice pick does this trick) in order to allow the rest of the water in the false bottom circulate into it, while contining the smooth rock so it doesn't scatter throughout the entire bottom. I attach some plastic garden edger around the outside of the egg crate so there is space around the sides of the tank that can be filled with smooth pebbles or other decorative gravel to hide the inner portion of the false bottom. Falls can run over cork bark, rock, or whatever you plan. Any splashing outside of the dish for the pool is returned to the false bottom through the substrate, so you don't have to worry about your pool dish running dry. Every so often, I siphon out most of the water and replace it--again from a simple aquarium air hose tube (and syringe to start the process) sunk to the bottom on one back corner. The falls, a tight fitting hinged glass lid and water splashed from the falls keeps the humidity above 80 all the time. There are many more high tech, better automated things you can do, but I like to keep it simple and relatively cheap. For the background, I have done various things, but one thing I like is a cocoanut fiber matt that comes in rolls) siliconed to the back. Any cork bark, pressed cocas panels (expensive, but I love to use them when possible,) can be siliconed to this and filled in with long fiber brown sphagnum moss, since cork bark is never quite flat. Epiphytes such as bromeliads grow great on this. You can just support them initially with bamboo skewers until they send aereal roots into it.
The substrate for growing terrestrial plants can be anything from an organic jungle mix, organic composte, milled cocoanut fiber, sphagnum moss, or a mixture of these. Don't use any potting soils with fertilizer, perlite or vermiculite. The perlite will get into your waterway, foul the pump, and vermiculite sticks to the frogs and just isn't necessary. Some vermiculites that aren't certified to be asbestos-free may contain asbestos, but that's not an issue unless it is airborn, which it wouldn't be in a damp terrarium. In any event, it has other drawbacks. Fertilizers of course would contaminate your water with nitrates and aren't necessary for good plant growth in a "semi-closed" system that is intended to become more or less "biologically balanced." Most tropical plants grow enthusiastically in a terrarium. My intial errors were to "overplant," and not allow enough open spaces.
The last few I've done, I've added a layer of small, smooth aquarium pebbles on top and spread Java moss over this. This gives the frogs a nice soft mossy surface to hop around on and keeps the soil from clinging to them. Homer turned me on to Java moss initially, and I now grow it in my aquarium section of the paludarium where it is a constant source of supply. (It grows under water or on land.) I keep it trimmed away from the pools because it will grow down into the water and clog the pumps.
These are just suggestions that have worked well for me, and certainly not the last word on vivarium building.
Your room temperatures sound better than mine, although 65 minimum is recommended. I don't know what kind of heater you are talking about, but I've had a couple of bad experiences putting under the tank heaters under the tank. In two instances, the heat has scortched the stand the vivarium was on. I do have some reptile type undertank mats pasted on the back of a few of the smaller tanks, just behind the waterfalls, and plug them in, in especially cold weather when the house temperatures may get too low. Whether they actually do any good or not, I frankly don't know. The ideal situation would be a submersible heater with a thermostat in the false bottom, but how long it would last and how you would tell when it failed, I don't know. Replacing it would be a PITA.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus
