I don't separate my Roos. And I have quite a few of 'em. The flock does range freely, so the roosters and cockerels have plenty of space to get away with not too much loss of grace (or feathers) if any of 'em do square off.
I have nine filly mature roosters and goodness knows how many cockerels growing up, but still part of the flock. My dominant roo, Carl, keeps everybody in line. After chicks have lived in their grow out pens for two weeks (or until they are large enough after two weeks to mix with the main flock) I will open their pen and let them join the rest. Usually the hens barge into their pen and go check out the coop, as they like to use it as a good laying space.
So the juveniles skedaddle and learn where they fit in the flock dynamics.
Some roosters have favorite companions and will meander together with "their" ladies - always aware Carl can have his way with them if he so chooses). Some of my roosters - fully grown roosters- have rooster buddies with which they roost at night, like BFFs, next to each other on a roost.
As so completely explained by RidgeRunner, everybody's experience with roosters is individual.
But the common idea that roosters will always fight and you cannot have more than one or two of them or they'll kill each other, is simply not true. Or so I've found, anyway.