As most others have said, they are great to have around to warn the flock of a predator, and many have said their rooster sacrificed themselves for their flock.
We have about 6-8 roosters free-ranging, one per pen x 6 pens, and rarely have issues with any of them. Someone's on here posting that is clueless about roosters, and best to listen to those of us who know.
Before getting a full-sized rooster, consider a bantam. They eat less while providing the same alarm/security that a full-size rooster provides. All else equal, their lighter weight is also less stress on the hens.
Regarding keeping roosters separate from hens, I never knew that was a thing. If a rooster gives hens grief, his life path changes.