12x12x18 Terrarium Advice

Hello, I want to preface this by saying that I understand that the 12x12x18 tanks aren't good for keeping many species long term, but I am still relatively new to the hobby and I'm looking for some advice. Currently I have my gargoyle gecko Cooper in a 12x12x18, but I have a 24x18x24 currently cycling that I plan on moving him into at the end of April/beginning of May.

With that out of the way, I've been thinking about stocking it with smaller animals such as thumbnail dart frogs or mourning geckos, but I would rather get advice from more experienced keepers than myself before committing to something and doing it all wrong. Again, I am aware that 12x12x18 tanks are not ideal for most species, but if it's possible I would love to know how.

Any and all advice would be appreciated, and thank you for reading!