Some breeders would recommend keeping them all in until 5 weeks others don't. I tend to remove bucks that I dont need any more earlier to give the does and the bucks I'm going to keep a bit extra milk for a while. I've taken bucks out at 3 and a half weeks and they live in a small group of bucks, the competition seems to do them good and they bullk up quicker than the bucks who are left with the mothers. It doesn't seem to have any impact on adult size or type though as they all catch up to each other in the end.
I think as a new breeder your right in getting advice from the experienced breeders on here but also go with what your instincts are, that way the mice you develop are fully a product of your methods and your stud.
I think as a new breeder your right in getting advice from the experienced breeders on here but also go with what your instincts are, that way the mice you develop are fully a product of your methods and your stud.