Last year, I had 8 cockerels and 1 flock rooster. I fully intended all along to replace my current flock rooster with a new cockerel...but none of them panned out. Just because you have roosters does not mean you have good roosters.
I agree with Ridge runner keep one in the flock 100% of the time, the rest in the bachelor pad. With the 8, I divided into 4 and 4 for the first cut. 4 went to the bachelor pad, and 4 stayed with the flock. Pulling out roosters changes the behavior of those left. I waited about 2 weeks and pulled out three more. Waited a while and didn't really like what I had, and culled again.
Do know that bachelor pads can work, for some flocks they work well, but sometimes they will work fine for a while, and then become a cockfighting arena. There just really no fool proof ways to keep cockerels and roosters. As in if you do this, set it up like that, you get perfect roosters. Sometimes it works, and a LOT OF TIME it doesn't.
Mrs K