Most pellet foods are fine, check to see that they are high in vitamin K. Stay FAR away from seed foods, like basic hamster diet, as these can lead to VERY fat mice (they are little piggies and eat the fatty bad seeds and not the nutritious ones hehe) Also you can get powdered or liquid vitiams that you add to their water... I HIGHLY recommend this. Been breeding mice for 11 or 12 years now, and in my experience the ones with the vitamin enriched water lasted much longer that the others. Temperature is also good to watch, keep the colony around standard room temp (23C or 68F) if they get a chill or a breeze they can quickly die, within a matter of a few hours. I know I've had a tub of mice in bed with me keeping them warm when the power goes out. Other than that, NO cedar, pine is fine, aspen just as good and nesting material a mst for the mommies, torn up paper works fine (nothing with ink in it) and don't expect her to actually nest in the nesting box, mine generally don't hehe. Hope something in there helped =) Good luck with the squeaker colony =)
Edit = Oh yes, mice become adults within a number of months.. 3 or 4 could be less of more depending on which type of mouse there are, some take 2 or 3 weeks, but those wouldn't be good, as the male will mate for 4 days then die (every mans dream right? Death by sex hehe) Generally plain old every day mice take around 3 months to sexually mature, watch you females for signs of estrous once they gel then you can put them in the breeding colony. (Gelling is the passing of the estrous cycle mucus, looks like little lumps of gooey slightly yellow jello)