Will this AP challenge a party of 6 without major modifications? Sorry if this has been covered, scanned the thread but didn't see anything.
just add extra monsters or mooks to every encounter to account for the extra actions a larger party can pull off and add extra treasure and you are ready to go. APs are designed for a party of four
There are several factors to this.
First, how experienced are your players? Are they adept at crafting characters that are able to compensate for weaknesses of other characters? If they are fairly new at Pathfinder and/or 3rd ed. D&D, then they may be challenged even without changing things.
Second, are you using rolled stats or the point system, and how many points are they built on in that case? My group has rolled stats and are the equivalent of 35 points for three of them (and one 54-point equivalent - she rolled really well, but didn't min/max her stats or the bonus for being human - she also uses a blowgun for her weapon of choice (and is a rogue), which seriously decreased her effectiveness). (The two NPCs are the equivalence of 25-point builds and aren't exactly overpowered.)
The points and experience are related, mind you. As I said, the player who rolled 17, 16, 16, 15, 15, 14 had only played Rogue Trader prior to this. She's still learning and while sometimes her character shines, in combat she's not nearly as threatening as she could be. The NPC Paladin, on the other hand, managed to do enough damage to a certain boss-character defending the Winter Portal so to have done probably half of the damage against it.
If you have new players to the game, I'd suggest giving them double max hit points for 1st level so they have a chance of surviving. Ignore the XPs and just level them up when the module suggests to level them. And increase the number of enemies by 50% for mooks and the like. If there are no mooks, then just give the enemy maximum hit points.
And then see how it works. If your players are trouncing this, then you might need to double the number of foes (the nice thing about tiny-sized monsters like sprites and atomies is you can have multiple in a five-foot square, so they make for excellent extra mooks to start with), and might even need to maximize hit points.
3 good seasoned 3 moderately experienced. I'm an old school 4d6 person no one has approached about using a point buy yet. All this info will be very useful, guess I may have to adapt on the fly a bit.
So for now, I'd increase the number of mooks by 50%, rounding up, and give them max hit points. If the players are steamrollering that, start using the Advanced Template. (The one thing I dislike about it is that it increases the armor class of enemies by 4. I think that's actually overkill for a CR of +1)
While there are multiple areas without fey as antagonists, given the versatility of pint-sized opponents, I'd be tempted to keep using them, especially in regions that are cramped. This will not always be the case, mind you.
Thanks again for the great input. I hadn't thought of the advanced template that will get some consideration. I'll let you know how it goes.
I'm running for a party of 5 right now, and to keep encounters adequately challenging I have been combining a lot of them or staggering them with only a few rounds to recover. We're about halfway through book one, and when the party reached High Sentinel Lodge, Rhokar busted out of the lodge (along with Ten-Penny Tacey and four zombified bandits) just as the party was polishing off the last of the five healthy bandits.
Later, Izoze chose to ambush the party as they were fighting Thora's doll.
My PCs are a mix of entirely new players and players that are experienced and who crunch a bit, but don't necessarily go for 100% optimization. So far most of the big fights have seen one or two PCs either in negatives or dangerously close by the end, and they seem to be enjoying the challenge.