5 cup cooker is considered standard for a family by the manufacturers. Assuming that you really like rice, you should make it fresh every day or so. If you want to "stockpile" rice for several days, then consider bigger cookers.
Depending how many meal you want to cook one time. I think even a 5 cup rice cooker is more than enough for 4 people for a single meal. Now if you want to cook for 3 meals-worth of rice for 4 people, then you will need a 10-cup rice cooker or larger.