lets see... im working with the same thing actually.
-a few peacock eels
-african butterfly fish
-a few banjo catfish and a moon light
-betta sorority
-assasin snail tank
i kinda like the single convict idea. i do like the idea of having one fish for a tank. im trying to get my parents to let me set up my 55 gallon so i can get a single senegal bichir to put in it. good luck with this
oh, almost forgot. brackish water tank. not at all difficult like SW has a reputation for being. it cycles like a FW tank with good bacteria in the filter, just add a lesser amount of sea salt (get s hydrometer to measure the amount) and your good to go... well, i mean in the sense that its like a FW tank so its not difficult. and for a brackish tank i recomend you look up wasp fish, also know as the butterfly goby i think, but its proper name is wasp fish.
Lol... Mine is a planted tank with lots of tropical fish and no filtration. Its a NO TECH tank. Only plain gravel, easy plants and fish.
You can use it as a fry tank too.