I never have aggression issues with my ASFs (and I have hundreds of them).

I have no experience with other breeds of rats or mice but the ASFs have ridiculous energy reserves and they MUST have a way to release that energy. I keep my 1.3 groups in 20L tanks with 2 wheels in each tank. It's rare for the wheels to be unoccupied.

ASFs are also notorious (and prolific) chewers. Give them something to chew on and they will love you for it! I toss in an edible log every month or so and toilet paper rolls on a regular basis.

The females WILL beat up on the males from time to time, but I have never seen them do any real or lasting harm.