Read old posts on this forum. My vivarium is exactly what you're thinking of, though I don't have any animals in it yet as I'm still working on keeping the humidity high enough. As for mixing day geckos and PDFs, I don't think it works. And believe me, I've researched it! Their temp. and humidity and even food requirements are all compatible, but geckos need a basking area with a heat lamp, and a UV light. PDFs don't need a UV light, and I don't think they would like a heat lamp. Also, you need a glass top to your tank to keep the humidity high enough, and the glass would block something like 95% (or more) of the UV rays from the UV light anyways, rendering it useless. If, however, you have it on good authority that you can mix day geckos and PDFs (pet store employees are not 'good authority'), then please tell me! I would love to house a group of D. azureus and a Lined Day Gecko (Phelsuma lineata lineata) in my 85 gal! I think that in order to make it work at all, you would need to choose the largest PDFs and the smallest Gecko, to avoid the frogs becoming food. Also, the small day geckos would be able to eat the fruit flies that the PDFs eat, as well as the occasional tiny cricket. The fact is, you have asked for a TON of information, as this is not a simple set-up. Have you done any other research? Why don't you decide exactly what species you would like, and research their requirements? And, once again, search this forum. I have a waterfall with a pool at the bottom and a stream, and yes, I did just carve some styrofoam and cover it with silicone and gravel (to make it look nice). But there are other ways. Some people use a hollow piece of wood for the stream. Just look around and see what you find attractive. There is a gallery side to this forum if you need inspiration, and you can also visit http://www.wildsky.net/vivarium/evivariu.htm, http://www.frogworld.nl/dutchvivariums.html, and the frognet gallery. Another good forum to ask questions on is www.kingsnake.com. Have fun!