C'mon now. You have to have some idea about a tank size. Okay....depending on your dedication to our hobby, maybe a 20g would be the next step up. I think bigger is always better, however. If you can afford the initial cost and have enough space, a 55 or larger would be my suggestion. Start with the tank size. After that, inspiration will come to you.
60g - Lot's of endlers and 4 P.Taeniatus Moliwe (and babies)
20g Long - a few endlers and RCS
20g Long - Chilli Rasboras, Scarlet Badis, RCS
29g SA biotope - many SA inhabitants