Festae. How many together?

I have been waiting to have the chance to own some red terrors. I now have a chance to get some 1 inch fry. I have four ordered but there are still two more available. I am just wondering how many I should order to ensure success of as many as possible surviving. I don't want to order six if I know they are just going to kill each other off either now while they're young or when they're older. I have 3 smallish (20 to 33 gal) tanks that I can place them in while they are young and as they get bigger I have a 72 gallon that I can move them into. their final home will eventually a 300 gallon tank I have. If I do have many survivors that get to adult size, how many would I be able to keep in a 300 gallon tank successfully with other cichlids, catfish and arowana. Thanks for your time!

Oops. Just realized I accidentally put this in the African forum. Gonna try to move it. Any feedback is still appreciated.