I had problems mostly with my girls. Right after I got two new boys, my brother accidently put them in the wrong cage. They were in the cage with my resident male, Dobbie, whom I was going to start intros with later. Dobbie didn't hurt them at all, he just groomed them.
But it could have turned out a lot worse. Had it been the other male that was here, he'd likely have injured or killed one. It was just his personality. He doesn't much care for other rats or people.
Depending on where you are getting the rats from, it might be a good idea to get one at a time and introduce them to your male. It depends on the travel involved. Or if your cage is big enough you could get three new ones and introduce one to your boy, during which the other boys will have each others company, and then later introduce one or both of them.
Congrats on your new boy/s. Pictures!! lol