2) Ask your flist to post questions in the comments.
"4, 6, 12 & 15 are starting a band together, what is their name and what kind of music do they play? Also, who's the lead singer, and what instruments do the others play?"
3) After your flist has asked enough questions, round them up and answer them using the 15 characters you selected beforehand, and then post them.
...This is either going to be really fun, or it'll send me straight to the Special Hell (tm). I can't tell which.