Bazza, use Jwalters' howto in changing the springs--that's what I used, and it was a good reference point. It should be in the suspension forum. With someone to help, and a cold pack of beer, the whole process shouldn't take more than a couple hours, maybe a little bit more if you're really being careful, and drinking more than wrenching.
Just make sure you torque everything down to specs, and loctite everything that you can. Most of your time is taking all of the other parts off and then having to put them back on to get to the fork tubes. I stuck with the the 10W oil. I'm about 185 lbs and usually ride two up with a 3 piece luggage set up and I still don't experience any nose dives when braking or downshifting, so that might be a reference point for you, if you're deciding to changing the oil wt.
As for the rear shock, pretty straightforward process--you can even take it off, and install your new one without taking off the rear wheel, while the bike is on its centerstand. Hope this helps!