Hi Bobby
The only fish I worry about mixing some community tank fish is your
JD. I know you dont want to return him/her but if you did there are a number of community fish you can add. Ive been wanting to see how my own australian rainbows get along with the JDs I have but the JDs are in a small tank since they are juvies and that may not give me a good idea on aggression. But with that said, you have a large tank and you can probably try this species with the JD in there. They are active swimmers that do not hide, get to be about five inches and are fast. I really dont think your young JD would bother them at this point and its possible that if they grew together they may get along. I hear that the pictus catfish get along ok with the JD in a tank, as our member Shawnie has had them together. She also has Silver Dollars with her JD as well. If she comes on line maybe she can give you some advice on that.
I have a convict with my JD who are about 4-5 inches long and the convict holds its own against them and pretty much gets along ok.
There are many fish that can get along with the Severum but Im not sure about the rainbow cichlid you have? Is that an African Cichlid?
wish I could help more, but Im sure that others will give you some good advice, best of luck with your fish and future tank mates.

EDIT: just checked and your rainbow cichlid is a central american fish and a pretty one at that! Says they are a peaceful fish, so guess you dont have to worry about community fish with it.