Hi
What you're refferring to is called a "Paludarium""Riffle
or river tank"Do a websearch on these and you'll find some info.Definitely check out the "Dutch Vivariums" They have moved them into art forms.Also take note of the dims of these setups . The old thread on this forum are another source.
Though I've kept aquariums and terrariums for many years
I setup my first paludarium last Feb. I used a 18x48x22 inch standard aquarium. It has a lot of shorycomings as a setup mostly not enough space.
I note that you want it primarily for animals so do a lot of research on the animals your interested in. Obviously it will have to be designed around their needs.
Do keep checking back to this forum.We all need help lol
Gary

It wouldn't neccessarily have to be a riffle tank, just a paludarium. Do read the old threads on this forum, as they will give you tons of ideas. Especially read 'Brainstorming on a Giant Orchidarium', and the threads on animals. For an amphibian, check out a Fire Bellied Toad. They are really frogs, but they like a larger and deeper water section than many other frogs, and they aren't the most terrible swimmers in case they fall in. Make sure you have some plants floating on the water or emerging from the water for them to sit on in case they do fall in, even if they are fake plants. Fish can be almost any kind of fish. Just make sure you research their needs thoroughly, and don't cheap out on a tank that is too small. You'd probably want a 30/29 gallon tank. That would provide an adequate area for a few fish and a few FBTs (they need to be kept in groups). Make sure the fish you choose like soft water with a neautral pH (7), because you can only use distilled/RO water with frogs of any kind. This rules out goldfish, guppies, cichlids, and many others. Also make sure the fish you choose won't be too big eventually and eat your frogs, because FBTs are poisonous. Bottom line: pick the animals, and then design the tank around their needs. You must be willing to compromise.

"RO water is absolutely pure, too pure in fact to be used as is. You must reconstitute the water by adding back a few beneficial trace elements, otherwise this ultrapure water will literally suck the ions right out of your animal! Commercial additives containing the trace elements are available"
Here's the full article -http://www.animalnetwork.com/reptiles/detail.aspx?aid=2178&cid=3691&search=

I'm not too sure of the truth on this but have read it other places as well in regards to salamanders and newts.

It could be true. For animals that spend nearly all of their time sitting or swimming in water, like salamanders, especially ones that come from environments with some minerals in the water, ions would leave their bodies in order to establish an equilibrium. However, RO water is still the only safe water to use, since rainwater can have pollution in it, and tap water contains chlorine and fluoride that are toxic to frogs and other amphibs. The best solution is probably to add a few of those trace minerals back into the water, depending on the animal(s) you are wanting to keep.