Your tank looks great, although a lot of fish for a 300 gallon, just think in the future when they are all adults... I have a 360 gallon and with only five cichlids in the tank, and IMO I could be trying my luck, lol... I have all South American cichlids, male & female Atromaculatum, Ornatum (not sure of sex, although I believe it is a female), female Festae & a female Umbee. Also I have 3 catfish. As I watch the aggressiveness they display to each other, I can tell that I would be able to put another cichlid in my 360 gallon tank...
I believe you have a good mixture although it would be interesting to see what happens when they all reach adulthood... Great job