The above is good security. A lot of people cannot do that, so do not add new birds. If you have a valuable flock, that is good advice. It is a real risk to add a bird, that who has no known history. You could either loose your flock to a disease he is carrying, or he could get a disease your birds are carrying.
If you want to risk it, and I have several times added rooster, however, never a rooster I did not know where he came from. Don't take anything you feel sorry for. Nothing sneezing, coughing, sick looking. But otherwise, I have just added a rooster directly to my flock. If he is younger than your birds, they may work him over and teach him manners. If he is the same age or older, they will be in love before morning.
It does change the dynamics of your flock. They will not look to you, but rather to him. I like having a rooster, but they can be a problem. One should not ever get a rooster, unless they can dispose of him, if he does not turn out. Some do not and can be aggressive.
Good luck
Mrs k
