Well according to the ARBA, the minimum you need for an individual weaned rabbit (or any of the smallest breeds) is 1.5 square feet. They also recommend 4 square feet for a female and her litter.
So it all depends on your rabbits needs. If the doe has larger litters you might need a second cage and split them up by sexes. If you are selling them at 8 weeks you can probably keep them in a single cage. If you are keeping them for a few months you probably want to move every rabbit you have into an individual cage.
It all depends on your specific needs; and if you feel like putting them in a larger cage there is nothing wrong with going above the minimum standards.
