The biggest trouble I can see with this is the different water requirements of the fish. Tiger barbs prefer soft, acidic water. Platys prefer slightly harder water with a pH around 7.5. Both of them can live happily in 7.0 though. African Cichlids, however, do best in very hard water with a pH of about 8.2. Even 9.0 if they are Tanganyikans. This would be the reason I wouldn't do it.
Life is not measured by the number of breaths we take, but by the moments that take our breath away.