Paludariums (Questions & Advice)

Amphibian/Fish tank
Hey guys I'm still working on that betta tank although all my plants died and i had to chuck them and add a filter . It's only a 3 gallon filter and its a 5.5 gallon tank so it shouldn't be too much flow for the betta. I'm letting everything relax for a few before I add new plants.

In the midst of it all we came up with a new project or rather potential project and I have some questions. Is there any way we can set up an amphibian/fish tank? Preferably something taller rather than wider maybe a 20 or 30 tall or something custom made along those lines. Are there any amphibians such as poison dart frogs, fire bellied toads, newts, basically anything the can be housed on top with fish in the bottom? Anything at all even a gecko (reptile, I know ) that can live in like a 50/50 setup half water half land. I can get creative and setup like a ledge or bridge or something so that there's alot of land space for the other animal whatever it may be. I just don't know alot about amphibians and reptiles. I will of course do my research before I get started, I just want to know what animal to research period. I'm already messing with filters ad pumps I have to see if I can find a way to setup an under gravel filter (I guess) that will feed water back to the fish via a waterfall in the upper "other animal" part of the tank. Any ideas are welcomed and pictures are a plus!

Keep your eyes open tonight for pictures of the betta tank I'll be putting up and thanks in advance for any advice!