1. The code is not too well document at the moment, but hopefully this will get better with vB3. But if you are a PHP programmer, you should be able to understand at least most of the code.

And if you ever need help, you can post in one of the help forums here and get answers from fellow hackers.
2. This thread, at vBulletin.com, has a lot of information about vB3:
http://www.vbulletin.com/forum/showt...threadid=45324
3-4. Yes that is possible, vBulletin also uses a template system, that lets you alter each and every piece of code that builds the forum. Check out the
admin demo to see how it all works.