I would wait until this group is like 10 weeks old, then clean out the brooder and get 3-4 more chicks, including your rooster. Brooder-raised boys without older chickens to teach them manners have a higher chance of being aggressive, which can be totally devastating to the peace and health of your flock.
I'd also go with a smaller breed to reduce incidence of injury. I adore Brahmas (and roosters, for that matter), but our Brahma rooster nearly killed a couple of hens just with his weight. Everyone says the hens can handle it, but that wasn't the case with us.
That's just my 2¢. Not sure if that advice works for you, but I really, really wish I'd heard it before setting up our first flock, so figured I'd at least float it your way. Have so much fun with your chicks. It sounds like a pretty flock!