I got the OEM centerstand and didn't bother to put it on myself since I was going to the dealer to pick it up anyway... doesn't seem to be hard if you know how to handle the springs or have a proper tool for that... once they are extended I recommend the coins trick but it's not the case in a new install... I messed with some springs on a slip-on exhaust on another bike and it was quite hard with just raw force.

XT660Z maintenance chart is for 10,000 km / 6,000 miles or yearly after the first revision. Earlier oil change can't damage anything and is not that expensive. I did oil changes around the middle of the interval but still got the gearbox fscked

As far for servicing where bought... don't think that's required anywhere in the world...