On the question of whether to use the band's PA or the house PA system: I've found for a folklore society that's used to bigger spaces, to just show up and let the society take care of the sound system. If it sounds like they're iffy on what they have, it's best to bring your own system, because that's one more thing under your control. We always have our stands and bottoms in the car, sometimes, I pack the mic bag just in case.