My problem with your roster, Coop, is that it's Bat-heavy. There's a wealth of characters to draw from beyond Batman villains and heroes. Something more balanced is JLA oriented roster; Supes, Bats, Wondy, GL, Aquaman, Martian Manhunter, and Flash. That's your original 7 right there. Then throw in some villains, maybe some JLI folks (Beetle, Booster, Fire, Ice). But having 5/16 of the characters Bat characters is just too much.