I would get rid of one roo. You couldn't free range them all at the same time if you want certain roosters mated with certain hens, and that could be a pain in the butt, trying to schedule alternating outings. And yes, one rooster should be able to service all of them. Now, you could run into problems if you get a LF rooster and he's trying to mate with little bitty bantam hens (just that he may be too hard on them..too heavy and such) and you can run into trouble if you get a bantam roo and expect fertilized eggs from LF hens (they may not get fertilized).
