Thank you so much @Colin_T ! This was quite helpful. I will go smaller on the dimensions now that I know that that would not be reasonable for an aquarium. I will also likely go with the first option of obtaining a species of live bearer and letting them live and breed in the tank before...
I'm fairly new to fish keeping, though I've been keeping reptiles and amphibians for years now. I've been thinking about making a 5'L x 3'W x 4'H custom Rio Grande biotope and I know for sure I want a group of 5 bluegills in it, and possibly a bullhead catfish, though I doubt catfish would do...