We got a 150 gallon aquarium that we plan to set up as a vivarium for frogs, geckos, etc.

We would like to put lots of plants and wood in it. As well, a waterfall running into a little pond area.

I understand that it is best to put down some sort of rocks or gravel (on the planted area) for drainage. However, what sort of substrate do you use to actually put the plants in?

Also, we really don't want to drill the bottom of the tank, but we need to figure something out for draining excess water. Any suggestions?

Thanks so much.

Does this mean mixing of herp species? Generally not a good idea, even in a large setup. If you were to take a chunk of the rainforest the size of your tank I doubt you would find more than one type of herp in that area. Insects on the other hand.....

I'll try to keep this short.

You have lots of options in a large tank, but I would do a false bottom on your setup. Reason for this is not having a way to drain excess water from the land section via bulkheads would more than likely leave you with a nasty bog. The false bottom would also be your drainage layer. Another plus of false bottom is that you need about 100 lbs of gravel for your drainage (you can use leca too but thats still about 20 lbs), that would make your tank atrocious if you ever had to move it. If your not familiar with false bottoms i'll help you out. Your entire bottom will have water and a small corner cut out will provide your pond.

Substrate- It all depends and I've recently adapted a controversial technique. I've switched to kitty litter (100% clay), now you may ask why. Well I'll tell ya If your doing a rainforest setup, rainforest soils are almost entirely drained of nutrinents, not drained but don't offer much. You'll notice very few plants growing on the forest floor, it's dominated by large trees which are covered in epiphytes. If you look at trees that are in poor substrates, not rich in nutrients like the rainforest, you'll notice they have huge root buttress' and shoot their roots out over the forest floor, not deep down into it. The reason for this is that the nutrients these trees get is through the decomposition of leaves. The roots are seeking the nitrogen let off by the leaves, thus they put most of their roots on the forest floor, not in it.
This is one technique, the on I am using, but you have tons of options. You can go simple and make it yourself or you can buy mixes. It really depends on what you want and the plants you choose. I'll give you some mixes later, substrates the second to last thing, right before planting.

For draining you can just siphon the water out or you can use the pump for your waterfall to pump the water out.

For the waterfall you can mount driftwood and have that as your waterfall or go the professional root and use marine epoxy. You have soo many options, just plan and research and look at other vivs for inspiration.