I agree with
@DobieLover I just saw that rooster in your photo, I would be concerned about the 2 being in the same space.
You have BSL and BO pullets - once they mature, they should be able to handle a large rooster. The Leghorns maybe not so much. I did keep a Leghorn with my large BO rooster, but he was not interested so I never saw him mate her. I had another very large BR rooster though that hated her and tried to kill her every chance he got (he's not around any more).
A LOT depends on his temperament, some are gentle, some are not - it's a gamble/wait and see sort of thing.
If you really don't want the rooster in with these pullets, do you have separate housing he can go into? He may be absolutely fine once he's acclimated with the pullets - monitor him closely though. I LOVE roosters so am a bit biased and give them every chance. I will house them separate for periods of time if needed and then retry things, change things up, but at the end of the day, the hens/pullets deserve protection.