Pick out species that don't look anything like each other to try and avoid any potential conspecific aggression issues. I've got a 72 bowfront all male, 11 adult fish, with no two alike, and working like a charm right now. Other than a minor chase now and then, no major aggression issues. Limit your choices of species to those that stay under 6" as well. Keep a few rocks situated to allow anyone being chased to hide. As far as lighting, substrate, and background, that's a personal preference. I have a black background, black substrate, and a dual T5HO fixture on mine with 10,000k and actinic bulbs.