1. Too early to know for sure about the '08 model since there are some changes, but '99-'07 is certainly a "go". It will raise the tail ~1.25"
2. If you have ditched the stock airbox for pod filters, it'll bolt in with no mods. If you're running the airbox, some light trimming along an edge is required. Search older posts on the Busa shock transplant or the FAQ for details. I'm running one, but I have pods, so don't remember the details.
3. The Busa shock is perfect for heavy riders. I'm 260 and my wife weighs more than your girlfriend (and just saying that might get me in trouble, so SHHHH!)
4. Better springs up front would probably be best, but I haven't done anything to mine except run the preload to it's firmest.
5. It's pretty straightforward. If you can break the nuts loose and remove a few bolts and cut a little bit of plastic without visiting the Emergency Room, you can do this. Changing the rear shock is pretty easy with the bike on it's centerstand - not so easy without one (a paddock stand is no help).