Keep in mind, the good breeding window for mice is only up to 9 months old. Their gestation is only 18 to 20 days, they are weaned by 3 or 4 weeks, and can breed at 5 or 6 weeks.
Recommendation is that they not be bred until they are about 12 weeks old. They should also not be bred any LATER than 15 weeks. That gives a female 6 months of high production, and then her litter sizes will drop off dramatically.
If you want to give her a rest, my suggestion would be to remove her from contact with the male and house her seperaely when she is visibly pregnant every couple of litters, and then give her a week off after that litter is weaned. Mice will rebreed as soon as a litter is born, so that when one litter is weaned, the next is ready to be born soon after. (Delayed implantation means they won't be born while the previous litter is still nursing).

Stages of development would be...end of week 1, fuzzies, end of week 2, crawlers, end of week 3, hoppers--end of week 4 to week 5, weanling, small adult up to probably a month old, medium adult for another month or so, then they should be fully grown. This is mostly guessing, because different individual mice will grow at slightly different rates, and reach different adult sizes.