First thing I do would be to get the OEM shop manual and any addendums to the manual if they exist. Also for a bike that old, a parts fiche is also handy. If you're lucky they may even have one or both in an Adobe .pdf electronic format. If the manual is out of print, try Clymer or Haynes. Makes it easy to figure out critical specs, dimensions, etc.
Do you have any maintenance records? Those would go a long way in determining what of the below should be done. It sounds like the bike is in great shape but I would check all the rubber/plastic parts for cracks - the intake boot, wiring, tires, etc. I would also check or even replace the clutch and brake cables. Next would be a compression test and there should be an acceptable PSI spec in the manual. Depending on how good the records are for the bike and how long it has been, you may just want to buy a piston and rings and replace them anyway. If there's nothing funny in the oil, I wouldn't think about splitting the cases. I would think about doing the fork seals and fluid because it may be old too. I would also plan on looking at all bearings and bushings and lubing or replacing as necessary. I would look at the back shocks but I don't know how much PM can be done to those; the manual should tell you that. I'd probably replace the air filter too. Lastly, I'd put everything together and make sure that all torque specs are correct, especially the foot controls. There's nothing worse than a shifter eating all the splines off of a shaft because it wasn't tight.
Hopefully this helps. Good luck and Merry Christmas to you too.
Best,
Greg