If you want a buff rooster, you can give it a try. I would personally wait until your pullets have come into lay. You don't want a mature, sexually driven rooster in with a flock of sexually immature pullets.
Then I would select a rooster that has already proven he is gentle with the ladies and...
It depends.
If you are breeding high quality SLWs, you will want more than one SOP quality rooster.
If your birds are just for layers and pets, you don't need to have any roosters.
If you like having roosters and have plenty of room in the coop (especially lots of roosting space) and run, you...