I always wanted one of these, but never really had the motivation and funds to make it happen. I usually get to the point where I'm looking at aquarium stands and I can never get over the fact that a $300 75-gallon tank needs a $150 tank stand. If only I'd known what I'd be spending on plants these days! I always wanted to have a terrarium with a miniature waterfall and stream in it. Never heard of a paludarium before - I'll have to add that one to my vocabulary. Doesn't even seem to be in my dictionary! But Wikipedia has it, and now I know the difference between aquaria, terraria, paludaria, and riparia. And even formicaria, vivaria for keeping ants! 'Cuz knowledge is power!
Basic terrarium practices apply, but you might want to look into things such as fountain supplies and the proper adhesives for attaching things like dividers and mounted rocks and wood to the tank. I'm sure you can find better instructions if you search around the web, and if you browse the greenhouse and terrarium or fish forums you can probably dig up some links on culturing certain types of invertebrates and fishes. Generally speaking, you'd probably start by doing a sort of dry landscape in the tank to come up with a plan, then you'd take everything out and attach your dividers, let the adhesives cure thoroughly, put in your fill media, sculpt water features and planting areas, put all the nonliving features in, add water, get a handle on climate control and water circulation, then let things settle. A few days after all that's done, you'd plant it and let the plants get established. Once the plants have grown in you'd add the various animals one by one, in an order designed to allow each niche to properly establish before introducing competition. Or, certain animals may be best introduced during or before the addition of plants - it all depends on what you want to have in there, and that's where you'll have to do some research.
I saw a very interesting forum thread - I believe it was on cpuk - depicting a sort of 'composting terrarium.' It had a dart-frog habitat on one side, and a big heap on compost on the other. Bugs fed off the compost on one side and then became frog food when they happened to wander through the permeable divider into the terrarium side. It's an ambitious project, but very doable and a great foundation for a (roughly) self-contained ecosystem.
Best luck!
~Joe