I'm asking for a friend

I have a question for all of my brothers and sisters that are Pathfinder 1st edition experts.

First though I'll explain the situation. I have a friend that's looking to run a Pathfinder Adventure Path. He has experience running other systems, some are even similar to Pathfinder. He's also even played Pathfinder a few times. The group will be about 4 people (not including him). The players all have experience with roleplaying, but some are more experienced than others.

So the question he has, has two parts. What books should he have on hand at the table? Also, what would be a great Adventure Path to run? He's looking for one that has something for all types of players (combat, exploration, npc interaction, even a romance arc is acceptable).

Thank you to anyone that can help answer this.

So as for the APs themselves, I recommend your friend do a bit of research on Google first. Honestly, that's the best route to take on this, as there are better written reviews than most of us could possibly give. When in doubt, the original Rise of the Runelords is a good pick.

As for the books to keep handy, the CRB is the only must have. Everything else is optional. That said, it's good to have a device that has AoN bookmarked, class/archetype notes printed out, etc.

If the whole group is new to Pathfinder 1e, I highly recommend sticking to either the CRB or at the very most, the books linked in the Pathfinder Reference Document (which is just the core books). Unless the group as a whole are good at picking up crunchy systems fast, I wouldn't allow much more than the PRD's contents. (Exception 2: converting everyone to Spheres of Power... but that's a long shot lol)