I suppose it depends on what sort of fish you want? from what I am learning most aggressive fish can grow quite large, however there are some smaller agressive fish out there.
SP44 are quite agressive and dont get too big
If you want aggression and beauty, I'd go for Salvini. Perfect tanks size and meets your requirements. You could have a pair of Firemouths or convicts in there with with them, but make sure you have enough caves and break the sightline up in the tank.
As River dog suggests, you MAY get away with a single salvini and 2 convicts, if you want a jewel as well, I would say only one convict and one jewel, although personally I wouldnt mix African and SA/CA cichilds. You will definately need to have plenty of seperate areas, either by using plants or wood and have some caves for them each to have their own area, even then you may have aggression issues particularly as the salvini grows.
Not sure what you mean by a small senegal bichir as they arent small, they can reach 12", although in that size tank one would be fine and shouldnt have any problems with the other fish.
Like with all cichlids it will be trial and error and dependent on the personality of the individual fish.
This is going to sound a crazy suggestion for a dither, but I have a red tailed black shark in with my cichlids, this is the 3rd tank I have had him in because he fights with everything. However in the cichlid tank he is fairly passive untill a fight between others start, then he dives straight in and seems to break it up, he is about 6" long now though.
ye i might keep my eyes out for one and see how the fish get along , i do like the look of themIf you keep your eyes peeled you can usually pick up a larger RTBS cheap or even free, because once they get bigger they can be a nuisance in the tank. I have had mine since he was a cute little 1" baby. But that is the downfall you can only have one.