Depends on your friends. Quantity, how active they are and at what times, and how much event running they're doing. I have a full list of 30 friends, but I never have more than 6 RBs active at once, and even seeing that is rare. I'm fairly certain this is due to time zone/schedule differences, as all of them log in every day.
By the way, for the event maps, default setup works for all 4, a bit of RNG is involved but it's not the ridiculous RNG fest of the previous event.