3step_paradise meets all of your requirements but there aren't any castmates. AC is flexible and works on a 3 consecutive strike system, we're very open to backtagging and events aren't planned very closely together.

The focus is on how characters explore and develop the world and themselves and so there's a decent amount of freedom. We're planning a big event for the end of April coming up that will last awhile but won't be fast-paced.