A few things as someone who's kinda high-up on Ps3e.
1) Don't disallow anything. Part of the flavor of PS is that you can find the wierdest and most exotic exceptions to every rule that every existed. Unless you're doing some massive overhaul of the system (like reducing the magic level, upping the technology level, etc), you should probably allow anything from red-necked Minotaurs to Halfling Paladin/Barbarians.
2) Check out
www.planewalker.com and
www.ps3e.com
3) About the only thing that isn't extremely well spelt-out in the Manual of the Planes is the flavor of Sigil and the place of the Factions. Take a look at In the Cage for a good take on how Sigil works as a nexus of the planes. In theory, you could ignore it, but I tend to enjoy the idea of a sort of city of babylon.
4) Check out
www.planewalker.com and
www.ps3e.com
5) About the Factions: If you go to the above websites' message boards, and ask about this, you'll get a TON of information. Mostly, there's no obvious way to introduce them into the game. I personally favor spending a feat to gain access to a faction power (from the boxed set, or more to gain upgrades from the Factol's Manifesto), and the more powerful faction powers being the purview of Prestige Classes, of which there could be many per faction.
6) Check out
www.planewalker.com and
www.ps3e.com
7) Oh, and if you're interested in the above way to do factions, take a look at Philosophies and Falsehoods soon from Silicon Phoenix Games. I use that system to grant powers. Other methods include making each faction a domain (forcing you to take a cleric level to gain power from your belief), spending XP or GP for faction powers (a-la Four Colors to Fantasy and some other systems), or simply granting the faction powers as a template with an ECL +1 (probably the most true to the 2e version).
8) Check out
www.planewalker.com and
www.ps3e.com
9) The plots of your DM should, if possible, revolve around the power and potency of what people *think*. This is a key flavor to PS, even more so than the Cant or the Lady of Pain. Anything that can enforce the idea that ideas, knowledge, and belief are the most important things in existence is a good thing. Because of this, PS plots tend to be a bit more cerebral than simple dungeon crawls. If you want, you can take a look at my award-winning adventure Eyes of a Child on
www.planewalker.com
And I'll leave it at nine, in honor of the Rule of Threes. But also, if possible, check out PS:Torment. This is quite a well done game, from what I've heard. But, alas, I've never played.
