i agree with wheekster, and have talked to you and told you on msn! hehe! he is probly showing he is maturing, and being with a load of girls, is showing himself off! when he comes to 3 weeks old, i think a separation is needed, but if he starts trying to mount any of your sows, separate him when you see it!
Purring is normal. If they wiggle there bum around when they do it, they are just becoming sexualy mature. However if they purr really low when you rub them around the rump, they are saying for you to stop it since they do not like to be touched in that area.