IMO your current stock level will be moderate when the O & SD's are full grown.
I recommend moderate stocking, but if your willing to put in the extra maintenance work a heavy bio-load/stocking entails...
One or two small SA/CA cichlids or one medium SA/CA cichlid would be OK.
For color? I would suggest perhaps a nice Turquoise Sev, very colorful and generally compatible.
I do not recommend mixing Africans with New world, to many differences in ideal habitats, water parameters and sometimes dietary needs.
With O's, many Africans aggression/speed often can be a problem, O's are often outclassed aggression wise and harassed.