If incubating 5 eggs, you could get anywhere from 0-5 roosters. There are no guarantees. It's a good idea to have a solid exit plan for any chickens you don't choose to keep. The options are sell them, give them away, or eat them. You really should have this figured out BEFORE you ever set eggs to hatch.
There are no definite "rules" for rooster to hen ratios. A general recommendation is 1/10. That stems from larger hatcheries that have found it to be a good ratio for maximum fertility. As Sourland said, a younger rooster raised within the flock could be accepted by the current rooster, but may grow up to challenge him. I have a friend who's younger rooster killed her older one in an ugly fight to gain dominance. There is really no way of knowing what will happen until you're in the situation.