Great adventure so-far, I tied this with my campaign and players were 8 levels. We are playing Planescape, so they have nice magic items, I only adjusted difficulty at Chapter I and IV's start, and we were fine. Party didn't steal at Chapter II, they hired and just dumped pirates before they could turn tail so I changed Chapter III start as Chapter V. My only complaints would be at Chapter II and IV, there is not much to explore within some plot locations, however it can easily be fixed. With combats as we were APL8, it took a bit of time. DMs can modify the difficulty a bit and it's fine to run with parties weaker than APL 13, there is also little sidebars that help you with those adjustments.