Why do you want a rooster? What are your goals for chickens and how does he fit in? The only reason you need a rooster is if you want fertile eggs, everything else is personal preference. Still, personal preference can be really strong. I generally recommend you keep as few roosters as you can and still meet your goals. That's not because you are guaranteed problems with more roosters, just that problems are more likely.
To answer your basic question, my typical laying/breeding flock is one rooster and between 6 to 8 hens. Over the years I've had two bad roosters, both became human aggressive. One time, when I first got the chickens to start the flock, I had 8 hens and one rooster. Two hens became barebacked so I ate them. The problem went away. It was not the rooster, it was the hens. My hens are not torn up, over-mated, or stressed out. You may or may not have problems with one rooster and one hen, one rooster and 25 hens, or one rooster and seven hens. You don't get guarantees with behaviors with living animals but one rooster and seven hens could make a really nice flock.
How old are your females and how old will the male be? Maturity is an important factor in how they are likely to behave. If your females are laying and the male is mature it should be a very easy integration. The rooster will mate a couple to show he is in charge and it's done. They are his flock. Again, you don't get guarantees with behaviors of any living animal but a mature rooster introduced to mature hens is usually about the easiest integration you can have.
However, if you have pullets and a cockerel instead of mature chickens it can be really messy. The cockerel may be driven mad by hormones and have no control. Pullets don't know what is going on so they won't do their part . As someone in here said, watching cockerels and pullets go through puberty is often not for the faint-of-heart. It can get pretty violent.
Adding a cockerel to a flock of mature hens can be OK but often it gets violent too. The hens may beat the snot out of the young brat or he may chase them a lot and force them. Adding a mature rooster to a flock of pullets often isn't too bad but if you can I'd add a mature rooster to a flock of mature hens. It is usually less stressful.
As to which breed to get, what are your goals? Why do you want a rooster? My experience is in line with Coach's, individual temperament is much more important than breed. If you want to hatch chicks, what traits do you want the chicks to have? If you want eye candy, get a pretty one. I would try to get one about the same size as the hens, though a bantam with full sized hens would be OK. Do not get a full-sized rooster to go with bantams. Many people do that and it works out OK but the bigger the rooster compared to the hen the riskier it is when they mate.