Any thoughts/specific tips on running this as my first AP as a GM ? I've heard its very good for RP. Got a group at work that is ready to start something.
Also, are all AP Paizo creations or are some 3PP ?
There are some 3PP. I can think of about 5 off hand, so I'm sure there's probably more.
All of the Pathfinder Adventure Path adventures are Paizo's, but there have been other companies that have written adventures run under the Pathfinder system. (Not necessarily all as extensive as Paizo's Adventure Path, but then again, not all of Paizo's adventures are either.)
As far as running Hell's Rebels as a first AP, I've read through it as a fairly new GM myself and I don't see it being an issue. But I have run adventures before, and I'm fairly well versed with the system despite being fairly new. If you're just starting out, you might skip the rebellion management system so you can have one less thing to keep track of, but even with rebellion management it should be fine. Hell's Rebels is well-written, so it shouldn't be too hard to follow.
Rebellion management is the only bad thing I've found with the AP. It's actually better if you let one player handle all of it, because trying to make so many decisions by group consensus is time consuming and tedious. But while having one player do everything is much quicker and often more effective, it means that the rest of the table is removed from the experience.
I'm sure you've probably already run it (as a group, I mean), but if you haven't, Rise of the Runelords is the gold standard for new GMs and players alike. Shattered Star (from what I ran before the game imploded for out-of-game reasons) is also very good.
That said, I'm really looking forward to running Hell's Rebels in a couple years (our group already has a queue going - we're in Book 4 of Iron Gods, we'll be playing Jade Regent after that, followed by Strange Aeons, and then getting to Rebels.) We also have/had a Wrath of the Righteous campaign that made it to Book 4, but I sadly think it's imploded as well.
Cheers all for the feedback!