Last year, somewhat by chance, I ended up with a whole bunch of Pathfinder books. After looking through them - especially the bestiaries - I decided that I liked them so much that I would like to GM this game at some time. Since then, I actually ended up buying a few more books... that said, I haven't got to playing this game yet.

Why? This game is scary - when it cames to the amount of rules. It crunchier than GURPS - the corerulebook has nearly 600 pages. And then, there are bestiaries, player and GM guides, advanced classes, books like Ultimate Magic / Campaign / whatever... I'm seriously overwhelmed.

And of course, before starting to GM, one needs to come up with a setting. That means decisions - on style and mood, on races available, on languages, on gods... And when you come up with gods, you need to create a whole cosmology for them... Again, more complicated than GURPS!

How to even start with this game??? Ugh...

Being a beginner GM, you could always just start simple.  Good players will understand that you would like to ease into the role and limit the character creation to just the basic core books to start and maybe allow the other non-core books at a later date when you feel more comfortable with running a campaign.  One piece of advice I gave to another fledgling GM was to use the introduction of another rulebook as an adventure hook...an expansion into a wider world for your party.

Most of the rule books are really just piecemeal articles that you don't really need to know very well. Skim over most of the specifics and then take a careful look at what your players actually pick. The SRD is your friend, I've spent a lot of time perfecting the ability to open manuals to the correct page, but for everyone else having a hyperlinked wiki available for all of the options is handy (the only way you can play a summoner in my opinion).

You are being too ambitious with your setting. What classes are available? What ever they picked! What races are around? Apparently the ones the PC's are have populations in the region, except the guy playing wolverine he's from some other region.

Powered by the Apocalypse (apocalypse world and it's contemporaries) actually have a really good guide on how to actually run games from the seat of your pants.

Crunchier than GURPS is maybe an overstatement. Isn't the collected page count of all the GURPS manuals something like 10,000 pages?

That being said if you know GURPS why are you trying to run PF? It's a steaming heap of un-fun filled garbage... IMHO

There are a lot of moving parts to Pathfinder, but it's much simpler than GURPS overall.  The thing you'll find quickly is that while there are a LOT of rules... most characters only touch on a fraction of them, especially at low level.  You need to read through the combat section a couple of times, check out the glossary, and skim skills and you're probably well enough equipped to run a module.

Getting started, I'd suggest running a module or two to get your feet wet.  Master of the Fallen Fortress is really popular for that http://paizo.com/products/btpy...-the-Fallen-Fortress and another option are the Goblins modules, which are just fun (and show the Golarion goblins in all of their sneaksy evilness) http://paizo.com/products/btpy...Module-We-Be-Goblins

For your first time out, you can force folks to use pre-generated characters (the goblins modules include them, and Pathfinder Society has a ton of them).  That'll greatly cut down on your issues with learning characters, etc.

Another alternative is if you have the Basic Set.  It has a scaled-down rule set you can use and it's very easy to make characters in and run.

By no means does anyone have to be aware of every single rule, choice and option in a D&D game. That's one of the nice things about level-based games: everyone only really needs to be familiar with the things relevant to the level at which they're playing. That's going to be a fair amount even at first level, since there can be a lot of basic rules, but it's still just a segment of what's necessary.

Then there's stuff that just isn't going to come up in your games. If you're not planning to involve seafaring, don't bother learning about the relevant rules, feats, items or monsters. Etc. That's one of the nice things about dungeon-based adventures.

The great thing is that you don't need to make all those choices yourself. Get some players interested in the general idea of a simple Pathfinder game, and then collaborate with them on the details.

And contain those details. Why do you need a cosmology at all? Not every game depends on that level of detail.

I can understand wanting those details, or feeling that they're necessary, but games really can get by on less. One thing they can't get by on is a frustrated, overwhelmed GM, so you'll need to find a balance. Remember that it's fiction, and don't hold yourself to too high a standard, as most of them are unrealistic anyway. You're not Tolkien, and you don't have his kind of time, or his goals. You're just playing a game. Let your guide be more modern stories where lots the details aren't written yet, because the writer (like most GMs) doesn't know how long the story will need to last. My bet would be that a lot of the stories you enjoy didn't initially have nearly the backstory they appeared to have down the road.

Hm. I can't imagine why I wouldn't need a cosmology? If I'm running the game in a setting that's supposed to be my own, I need to come up with my own gods (otherwise, there won't be any of clerics to choose from). And if I come up with gods, these gods need to make sense conceptually. Meaning, I need to create some sort of cosmology...

It's the same with creatures like demons, devils etc. I feel that if I include them in the setting, I need to know where they come from, so that I RP them faithfully. And that means creating the history of the universe... Uh.

One solution I have is to decide that the gods are basically unknowable and that there might hundreds of religions out there worshipping their own gods. So, a cleric player would get to create their own custom god during character creation...

As for having to choose races beforehand: let's say that I run the first adventure as a goblin encounter. Then, I decide that the setting is supposed to be serious, gritty and dark... But that doesn't fit with that first adventure, which included goblins! Which are funny and cute and cartoonish! So, I need to know beforehand whether I include goblins...

Anyway, thanks for the advice! Keep it coming...

BTW. Reading the rulebook right now. I'm on page 30 and so far, so good. Although I don't get why sorcerers use Charisma to cast magic... And why Strength determines the ability to hit someone in melee. Some of these rules are weird...

There's a good reason its nickname is Mathfinder.