it should be 10 hens to a rooster.. Your hens will get overmated, I do believe. Or the roosters will fight all of the time. I will be in the same dilemma pretty soon.
we had a production RIR Roo that was AWESOME!!!
I had to re-home him because he was such a baby that my bantam rooster picked on him relentlessly. We held "Rose the RIR" every day until he got a new home at 10 months old.
Rose is the Rooster in my avatar.