I don't know the answers to these questions for sure (hopefully Auburn can chime in to let you know), but I think I remember reading that I--- is most common development and II-- is the second most common. In terms of the distribution of the types in the general population, my guess would be that we don't know that yet because the people who have been typed are all either famous people or people who are interested in CT and have paid to be typed, and those are both fairly specific populations that wouldn't be expected to have the same distribution of types as the general population.