They can recover from some pretty awful injuries given time and support, but that is your call based on what you are seeing and how much time you are willing/able to give her. 10 -12 hens per roo is a good starting point, that number can vary depending on the rooster itself and his temperament and personality. Not having enough hens results in ratty looking, or injured hens. A cockerel (a male less than a year old) is a rude, clumsy, inconsiderate oaf most of the time, whose hormones rule his behavior. Some mature roosters can be a joy to have, some not so much. You may need to separate the cockerels if they are hurting the hens, let them mature where they can't do any harm. If you don't want to hatch your own eggs, or plan to range the hens where a rooster may provide a bit of early warning system, then no need to put up with any of them if you don't want to. I actually rather enjoy my roo's, but I only keep the best ones.