Honestly, every rooster is different, every flock is different. Some roo's are terribly rough and tear up the girls and some don't. Some are just sweethearts. Age can be a factor too, younger roo's tend to be a little rougher as their hormones surge. The 'math' is a guideline, not a set rule, you have to do what works in your flock. There are pluses and minuses to keeping roosters or not keeping them. If you take 4 or 5 birds from an established flock they are going to have to reset the pecking order in the new flock. You won't really know who's high or low until that happens and you won't know where they were in the other established flock. If you raise chicks, that happens gradually as they are all together from the beginning and it will be less 'dramatic'. It may go perfectly smoothly, but you will not know until you do it. If you think you want to have a rooster then take him and see how it goes. You can always remove him later if he's mean (I'd walk through his flock and pick up a hen or two and see how he reacts first - if he attacks you, then I would not take him. Period.). Also, IMHO pre-made coops usually are way too small for the amount of birds they say they will hold, enough space is very, very important and becomes more so with a rooster. Your hens need to have room to get away from him if they choose. Also having a roo comes with different possibilities and you need to be prepared for those. As previously said, it can be hard to re-home a roo, so you need to be prepared to do whatever needs to be done if you decide you don't want him or can't keep him. If you don't want a rooster or are not sure, then I would pass on it. Keep some hens for a while and see how you feel about it, or raise your own chicks, you can always add a rooster later if it's something you decide you want to do (if you add chicks periodically then odds are you will eventually get an 'accidental' roo). I have 23 in my flock right now, two roo's, everybody is very happy and gets along, but I'm very choosy about what roo's I keep. I kept hens for several years before I started keeping roo's in my flock. Now I can't imagine not having them.