If breeding mice you will want a rack type setup with good ventilation. Tanks make Mice stink way faster.
I currently breed 20 groups of 3.6 and i never take out the males ever. This produces me 500 or so mice monthly. Be sure if you over produce you have a steady buyer for the extras.
Females usually dont get pregnant till thier 6-8 weeks old, but males will start mating at 4 weeks old if they were ready.