When I kept mice in 10 gallon tanks, I found that 1.2 or 1.3 females was enough, once the litter got to weaning age, and they were then moved out into another tank. While you might be able to keep weanlings in with the adults if you are killing a lot as pinkies or fuzzies, if you want most of them growing up, they will be pretty crowded with all the babies from even 2 females in a 10 gallon by the time they are 4 weeks old.
If you are going to buy more housing, I also suggest that you consider inexpensive rubbermaid type containers. They are cheaper, lighter weight and much easier to clean than aquariums. You also get more floor space for the same amount of money, so unless you wnat to be able to see the mice, the rubbermaid type tubs are great. We just replaced the lids with a wooden frame one covered with hardware screen and put a couple holes in one side to attach a water bottle with cable ties. We use the tall ones so there is room for a wheel and an igloo house, but you can use flatter ones, you just have to attach the lid more firmly. These house breeding groups of up to 1.6 and babies until weaning age, when all the weanlings go into a separate tub.
mary v.