I think you've had plenty of discussion on what kind and ratios of roosters, so I'll talk a little bit about temperament. I think some aggression issues are genetic. I think mean roosters can pass that along to their offspring. But I also think you can "condition" them when they're little. When I notice that a chick is a cockerel, I stop handling it immediately. When they're old enough to be out and about, I let them know that I am the boss. If I want to move from one side of the run to another, and a cockerel (no matter the age) is in my way, I walk right through where he is. If they're outside free ranging, I will walk toward them and keep walking until they move out of my way. If one comes toward me, I walk toward him until he backs off or moves away. Move him away from the food when he's eating, just because you can. Meet every challenge with confidence.
I think the important thing is to start before they ever get old enough to go on the offensive themselves. A couple of years ago, I had a buff rock cockerel. He would give me the stink eye now and then, and I would stare him down. He never tried to invade my space, but he'd sometimes follow at a distance. I'd walk toward him and back him off. One day I was "helping" a pullet into the run so I could lock them in for the night. A nudged her with my food, and she made a fuss. That cockerel came running, saw me, gave me the stink eye. As I stared him down, he decided that he had something more important to do on the other side of the run. Sadly, he was killed by a predator while protecting his flock before he could grow up. I would love to have seen what kind of rooster he would have made.