Well, if it's taller than it is wide, maybe a Tree Frog would be more suited for it, although, perhaps you could house a Terrestrial frog/toad and make it really unique, adding tiers/levels, though that'll take some work .

If I had a tank like that, I'd probably get a Bufo Marinus, as they need a lot of space and I've only got a 10gallon for my 3 Coqui Antillano. I'd make two levels, the bottom one being majoritively water[as they breed here], with an undergravel filter[maybe] and the top half Terrestrial, with lots of plants to hide in and a nice heat light for it.

Yes... I've thought about it alot

Something like this;
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But larger[like yours] and with tiers.