Based on what you say regarding mileage I get the sense the owner believes its a "minter," but in reality only doing 80 miles per year and leaving it sat for the rest of the year could probably create more problems than its worth. It may look visually good, but with everything having sat for so long on a regular basis how good does it run? If you can't take it for a run, I'd rather take a punt on a cheaper one from a dealer so at least you've got some "protection." Fazer 600's, as you know, are fairly common and easily modifiable. There not a bike I'd want to pick up a headache version of when there's plenty on the market.
Regarding the noise that you mention I wouldn't be overly alarmed. Many people prop their bikes up on the centre stand and convince themselves they've got an issue, but most of the time they don't since that's not how the bike is meant to run. Much in the same way running the bike in first, very gently, on the centre stand is pointless because the chain isn't under load etc (although this may be useful in this case to check what its doing an pinpoint the noise properly making sure NEVER to release the lever all the way, mind).
You'll want to take it for a run and make sure the chain hasn't been over-tightened and the noise isn't coming from inside the front sprocket cover and the bearing damaged (worse case scenario). Check rear wheel bearings also.
Other than that I'd just replace the chain and sprockets from the get go to save the headache. I paid £170 recently for a D.I.D from a dealer, so aim for £200 at most and if he wont budge then leave it alone.
Cracks on the inlet rubbers are about the only other thing I'd look out for (common, but how damaged are they)...
HTH.