Here is a few more things to think about in your world when you are creating it.
1) Technology. I mentioned magic, but what if you want some steam punk type objects in your fantasy world. Think hard on this. If you give it to your players, your bad guys need to have them too, and that may let things to get out of hand. Another way to put tech in is simple things, like water flowing into houses, sewers, gas lights, but no weapons.
2) What classes do you want? We always have the core classes, and with Pathfinder, a few newer ones. But my husband and I have said no to prestige classes. They are not balanced, no matter what the creators say, especially if you have your own "Brian" in the form of my husband. If there is a loop hole, he'll exploit it. If you do want prestige classes because one player really wants one, I suggest you have a bad guy, (or three) with the same class or one that can counter that class. It may seem unfair to the player, but it really is the only way to balance out the prestige classes.
3) How does the hierarchy work? Do you have Kings and Queens, Emperors, Democracy, village elders, clans? Is there a mix in your world? This is important so your characters have an idea where they are in the scheme of things.
Part III tomorrow