About teambuilding for this type of event: for non-challenge songs, since the bonus is for event points, should I try to fit as many bonus characters as possible on the team regardless of band compatibility? From what I remember of the event point formula, increasing the event point bonus is worth the tradeoff in team power, but I could be wrong.
For the challenge songs, since the bonus is for character power, it probably makes sense to forget about character bonuses and just go for whatever team can get the biggest area item boost (and still has enough score boost skills).