You should first follow a 30 day quarantine. No matter how healthy the young man looks, he may be harboring an illness or parasite and I know you wouldn't want him making your girls sick.
Once the quarantine is up, it's best to introduce him behind some sort of barrier (fence) so that they can get to know each other without danger of bloody interactions.
When all seems to be going well, go ahead and put him with your girls; preferably at night. Be there in the morning to see how things are going. You should expect some scuffles - the head hen is not going to want to give up her spot, but as long as no blood is being drawn it's best to let them work it out IMO. It might be best to walk away at this point. Roos can be a bit rough when they are first claiming their domain, but it's nothing the hens can't handle.
Him being part bantie is not going to make a difference. It's not the size of the roo, but his attitude that counts. Fertility might suffer, but he can take care of your girls just fine.
Good luck.