I did 20k on a run with my Z that already had 20k on it. There is not much to worry. Only things that you have to take caution is wheel bearings. Take spare bearings with you when you can't get a hand on them on the way, better already change them to new ones. Because they tend to rust when you do a lot of river crossings and the bike seems like it was used offroad. Most important is to lubricate the steering bearings (already having my third one). Oh and a spare spark plug could not be wrong (best take an iridium).

About the tyres. Don't forget the tyre valve tool and some tube fixing pads. I forgot the tyre valve tool and bought it after the first change of tyres

About tools, don't forget the hex key set. Otherwise u will be screwed. You won't be able to fix anything without an hex key set.

It seems like you want to drive 16k with a K60 Scout. If you go on hot tarmac they wont last this long. Better try to find a source you would be able to change the tyre after a maximum of 10k if needed. It's more fun and safer with a tyre that has some tread left. I also believed a Mitas E07 would last 20k (I read about many who drove this far) but had to admit that it was gone after only 9k (front was almost flat and the rear maybe would have lasted longer). Maybe its possible to do 16k with a Mitas E07 in the rear and some other type of tyre in the front.

And about the cush drive rubbers. Just check from time to time if the sprocket has any play and cut a tube and put it in the gaps off the rubbers (there are many threads that explain it). Spare rubber would just take to much space. If you dont wanna care abt the rubber take the polyurethane rubbers form Hunday, he is from Cape Town ( http://www.xt660.com/showthread.php?t=21410) if you send him an email he responds quick (he doesn't answer PM's)).