He's a very young rooster. 5 months is still a baby. He's still in self-centered mode and likely won't be protecting them or finding them treats just yet. Perhaps another month or three.
Also, if he is a rooster that grew up with your hens (meaning your whole flock is the same age), I've read that roosters in such a scenario are often more aggressive. Roosters that grow up as chicks around adult hens or other roosters are taught "lessons" by the adults, usually in the form of pecking to help them learn their place in the flock.
If you've never seen chickens mate (or ducks, now that looks like rape, but it isn't, according to wildlife experts), do know it can look and sound a little rough. Some roosters are rougher than others. I don't believe it is something you can "train" them to do differently, but you can control a rooster's behavior to some degree, by the number of hens he has available to him.
The hens are also getting used to a rooster. It's a shock to them at first, but they will get used to it. And if they like the rooster, they will start "presenting" themselves by laying down and will have their tail feathers turned to the side (you may not notice this behavior for a few more months).
Also, you haven't mentioned how many hens to I assume is just the one rooster is? The "general" rule is 10 hens to every 1 rooster, but some people get away with more or less than that. If you only have 3 hens, then that could be a problem, as your rooster will very likely oversex them. If the hens start to look beat up, they're getting oversexed.
As for aggressiveness of roosters toward people or other animals, you will have to be the judge of that. To us, it's not okay for a rooster to attack us or be a bully to all the chickens. Some roosters are just mean. When we have mean ones, they end up in our freezer. We only keep the nice ones, and not too many. Also know that many consider a rooster's sexual maturity to come fully blossomed around 2 years of age.
DON'T shoot him with a BB gun, not unless you intend to put him in the freezer. It would be easy to miss and injury him or a hen with an errant shot. He's only doing what his instincts are telling him to do and I seriously doubt you could train this out of him. If he is truly brutalizing your hens, then you may need to get a different rooster or get more hens. But I'd suggest giving it time, so he and the hens can get used to it. Assuming you don't have too few hens to your one rooster.
As for the dance, I've seen video of what you talk about, but none of our roosters have ever danced for our hens.
