I recommend ZERO roosters unless you are planning on raising hatch-lings. 2-3 roosters is even way worse as that allows them practice fighting with each other. They tend to get meaner and take the fun out of visiting with your hens... or even collecting eggs, as you will always have to make sure they are not sneaking up behind you to attack. We started with 14 hens and three roosters. The roosters were welsummers,,, the hens welsummers, bard rocks, and australorps. The roosters will constantly challenge each other (and you) to see who is the dominate alpha. Seems they only work together when combining to attack me. As far as hen protection goes.. my experience is that my roosters are the first to skedaddle when chaotic danger approaches. They are also capable of tearing up the back of the hens when mating (we had to buy a couple of our hens protective saddles).
We paired the roosters down to one, and finally got rid of the last rooster a few months back. WAY more enjoyment visiting the hens these days, and my wife and kids can sit in the coop area without fear of being attacked.