Make sure you have a place to separate them before they start trying to mate. They chase, grab neck feathers and don't let go, make pullets scream. And all will try to mate a single pullet that they have caught. It's quite a rude awakening if you aren't prepared. And they will go after the weakest, over and over. Many of them peck at the top of the head. I have girls with chunks missing out of their combs. The boys are quite vigorous when they first reach that age. After they mature a little... they will call the ladies to treats, drop a wing and do a little dance shuffle as well as a handsome little serenade sound they do. And they learn that they don't just take it when they want, they learn to take no for an answer on occasion.
It also help if your ladies are are older before you get the boys. They are more confident and able to fight back if they want. Verses pullets of the same age have no chance and the boys are ready to mate a bit before the girls. They always mature sexually a bit sooner in my experience.
I don't think any of the roos will be too big for your girls unless they are bantam. I even saw one person who's full size roo stands on the ground at the back and gently mates her banty.
You won't know that until they get up there close to 8 or 10 months before they actually start protecting the hens and possibly attacking or showing human aggression. Some are just aggressive from very young. But there is hormonal changes that take place that bring out the different natural behaviors. Did you see the links to rooster training?