So I have 8 players for this AP.
I know that's pretty crazy but after years of struggling to get 3 players at our table I was determined not to turn anyone away after PFS introduced us to a whole lot more local players.
Anyway - any tips or thoughts on how to scale up the encounters appropriately? Adding more minions is probably the simple way for many encounters, guess I'm going to need a variety of things for the duration of the campaign
They are currently halfway through part 2 of book 1 (so about to go into the basement of the plague house)
I'm running a table of 6 players, with a 20 point build, and overly capable at making builds, so from that experiance, I would recommend scaling every encounter to include 50% more mooks, and give foes 100% HP / HD instead of average. Also liberally add the advanced simple template on almost everyone. For single foe combats, either add mooks or add the agile mythic template.
The only caution is a few random encounters can scale in a odd way, the Titan Centapede in book 3 can trample for an obscene amount of damage, or ice worms in book 4 can have a deadly death throes.
In addition to what Galnörag said, I highly recommend you familiarize yourself with this page. Class templates let you, essentially, convert their racial hit dice to class hit dice, giving them class features without giving them more hit dice (because that would just be overkill.)