We house our mice in ratios of 1.7(1 male to 7 females) - We let them live together pretty much all the time, once a female is very pregnant, and near ready to birth, we move her to a private enclosure for her and her babies. I've heard that the other rodents wont bother the mother or her babies, but that way, babies never get mixed up, and the male wont instantly re-impregnante the female. The dimensions we use are about 21x16x5(LxWxH) for their housing. The rats are in larger enclosures 24x18x8 and we keep them at ratios of 1.3, and follow the same procedure of femlae isolation before birth.

And as for the forming friendships/colonies thing, i believe this to be true, we leave our males with their females. And if the colony crashes, i'd reccomend feeding off all the mice, and starting by forming a new ratio.