Sounds like a fun project. Salamanders, small frogs, tree frogs all come to mind. As for fish I'd stay with smaller docile species like mid size Tetras, Black skirts, bloodfins, H&T, Bleeding hearts and the like. Some of the smaller varieties of rainbows would be nice too. Long fin Danios, Swordtails, Mollies.
Stay with salamanders and frogs. The toxins from toads and newts would not do well with the fish. NO turtles as you've already surmised your fish population will dwindle as your turtle grows. LOL Try to keep your inhabitants of similar adult size to minimize losses due to eating each other. Dwarf aquatic frogs, Eastern and/or California Sallies, Great Plains Narrow Mouthed frogs, green tree frogs would all be good choices with the above fish.
This kind of assortment would give you lots of activity for both the land and water but excellent filtration and frequent water changes would be required for the health of all concerned.
Another suggestion, when dividing the tank use plexi glass. Mount one piece horizontally towards the upper portion of the tank and another vertically as a dam. The area underneath would add more swimming area for your aquatics. Another trick I've used to disguise the land mass area is to silicone a mixture of various sizes of aquarium gravel and sand to the outside of the tank. This lends a 3D effect and hides your substrate mix and plexiglass. You can also add this to the vertical piece of plexi inside the tank. Keep it irregular looking for a more naturalistic effect. Even the back of the tank, adding bits of aquarium plants or better terrarium moss(sphagnum) glued in place is sweet. I have one like this in the shop but the rotten little kids like to pick the gravel off the outside. I'm in the process of making a new one. People ask all the time how I got the holes through the tank.
Hope this helps
BigT
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Hope this helps.
BigT
There is a difference between ignorance and stupidity. The ignorant can be taught, stupidity is beyond our control.