So what I would do is get the tank going, ie if you can't seed it with other tanks get say 6 fish at most. Watch those levels.
Then the next question is do you want to go with younger fish and let the grow up together, or are you will to spend the money on attempting to start with some larger fish, and seeing how the get along?
Either way I likely would at ~12 make sure the tank keeps up well, then 12 more. After than well I honestly would go by looks and water parameters. My large tank now appears packed when they all come up to eat/greet me, but when they are swimming all over it isn't a paroblem. (I have ~40 fish ranging from ~11 inches to 3 inches in that tank). My sump is 55 with enough bio media for say a 800 gallon tank... But well it makes it so I never see any bad levels even if I skip water changes for much longer than I should. (I try to do water changes ~once a week.)
So then the mix it wont really matter for you... For the peacocks make sure to not get similar colors else the other males really wont show. Haps it is OK to have say two of some, but depending on the type the sub dom may show less color. But honestly don't get the same fish twice unless they really do look very different when they are an adult. (Say like rostratus, though they are bigger than the fish you are looking at.)
