You might as well set them up in breeding groups.

That way they grow up together and theres no stress later when some are removed/introduced.

The only reason you would not want to setup breeding groups is if your worried about them getting pregnant too young. But if you're worried about that then you have to seperate the males and females for another 8weeks at least cause if you're gonna wait you might as well be sure they're 12weeks old.

But personally, I wouldn't worry about as long as they're healthy and you feed your first time moms a high fat/calorie food mix.