I can understand that you are very excited with your new aquarium but the two species you have in there already are both capable of reaching a relatively large adult size 8"+. Realistically there isn't enough room for multiple territories, though this upgrade was quite substantial for you. Personally i'd think about removing either the jd or severum and then add a group red rainbow fish (Glossolepis incisus) these can get to around 5" and are stunning sight in a well maintained and appropriate aquarium. A species that would compliment this suggested stock imo would be a single L200 green phantom.