I made the website and the forum style so hopefully I can answer some of your questions. The forum style was actually made first, and the website was coded up shortly afterwards using the same HTML / CSS / Images as the forum style. They're not "integrated", although it was designed to make it look like it is.
Yes, the theme was purchased from PixelRaider.com, a site in which I own and operate with one or two other people. ~smile~
I started FP (with help from efc2009) about 20 months ago now and we started on a free phpBB2 host. What drew people in was that there wasn't many other phpBB advertising forums around which made us a bit unique and we were the only one at that time (that i knew of) being active at the host we were using which meant we got alot of people from the support forum to join as the forum was unique and alot of people found it a good idea. That gave us a good userbase from the start and by constant promotion we have got where we are today.