Basically, the Hoffmann Institute investigates the paranormal. Which also happens to exist, as you may have noticed...

Unfortunately, there's something of a "need to know only" mindset within the Institute, so you rarely get told anything that doesn't have a direct baring on your current mission, and sometimes less than that...
As for Advance Classes, all the classes in the SRD are available, along with the Battle Mind and Telepath and the Wild Talent feat. Magic based PrCs will also be available, but I need to check them over quickly to decide which best suits my idea of the setting.
As far as non-core books go, I don't own any, but I'm happy for people to use stuff from them. I'll need to be sent the rules details so I can OK it, but as long as it looks reasonably balanced and fits the setting, it should be fine.
Oh, and thanks for the heads-up on the web enhancement. Hadn't spotted that, and it will indeed come in useful