get yourself 2-3 marbled gars, they technically arent gars but look just like a minature spotted gar, max out around 12" in length. datnoid is another great option and a pair of severums like you're planning could look nice
I was also considering getting one hepsetus odoe (african pike) and one red tail chalceus. Could this two get along? Any comments on those two fish? One lfs near me has a beautiful chalceus, but some of the other fish in the tank have ich and I don't have a hospital tank. So needless to say its not happening for that one.