well, the number of people on a base depends on what kind of game you're planning to play. For a skirmish one the single bases should be nice, but for a larger game you will need 4 or six pieces. If you want to play Impetus you might like to put more than 15 minis per base! =)
The only thing i can say about the base shape is to make it thin! When you have such a small miniatures, the high base is quite a big step, and separates the minis from the ground too much. Furthermore, any kind of scenery you're having will look to small, since the figures are "high-heeled" by the base!