Kenyi are super aggressive, I would try a ratio of 1m/as many females you can fit in the tank. Having enough females will prevent to beat the snow out of anyone who doesn't want to breed, he can just move on to the next female. You'll need a few extra tanks to remove holding females, and to keep fry at different sizes. You'll also need a place to get rid of fry, kenyi aren't really a favorite with alot of mbuna keepers since they're so aggressive.