Rubber Ducky guy |
Hi Leojen.
Every adventure path has an advancement track where they suggest what levels the players should be to tackle each chapter, which sorta decides the milestones for you.
For the Haunting of Harrowstone it's the top right corner of page 7.
Text is here
Quote:
Advancement Track
“The Haunting of Harrowstone” assumes the medium
experience point track, detailed on page 30 of the
Pathfinder RPG Core Rulebook. Characters should be 1st
level when they begin the adventure. The PCs should be
nearing 2nd level before they attempt to venture into
Harrowstone itself, achieving 3rd level before they delve
too far into the dungeons below Harrowstone. By the
adventure’s conclusion, when they exit the prison, the PCs
should have reached 4th level.