Thanks for the pictures, I've not seen some of the pictures before either. As for the drama, it started filming already, Pi mentioned about filming in his recent jweb entry. Glad to know he's occupied doing something, the folks over at LoveSong forums already announced that they're going to sub the show.
Pi is so popular because... I don't think I can fully answer the question,

many factors I guess. Anyway, a good indication of how popular the artistes are in Japan will be taking a look at the magazine/Oricon polls that are conducted on a country wide basis. Folks like Yamapi and Kame(KT) do appear high on the list in such polls, the same cannot be said for the other JE members. Also, the sales volume of singles and such do give an indication of how much 人气 an artiste has. I suppose like the Chinese entertainment industry, the extent of one's popularity is not really measurable but it can be felt as long as one pays attention to the industry.