I don't recommend changing the spark plug until at least 10K miles. I changed mine at 10.5K with the stock NGK DPR7EA9 (18mm Deep socket). I don't recommend using anything but a stock plug as there is nothing to be gained.
The reason I don't recommend going in under 10K is many scooters will never reach that mileage and many people knock off hoses and damage things and introduce problems when there was nothing wrong in the first place. The frequent maintenance schedule is setup so you visit the dealer more often. Nothing wrong with that but the plug and other stuff doesn't need to be changed ever 3K.
Only recommend changing the oil ever 1200 mi. Although, I forgot and went 4K mi between changes once!
Many may disagree with me but I out ride most scooter / motorcycle owners by a factor of 4X. Right now my scoot has over 18K on it and still runs like it did when I got it with 2,600 mi. Start, idle, full throttle on the highway, cooling, etc 0 problems except...
Repeatedly, cracked / welded the exhaust.
Cleaned contact switch for rear brake light / start up - still acts occasionally.
Cleaned carb / clogged pilot jet many times - original owner let it sit with old gas. No repeat problems in the last 5K miles.
Broke / fixed mirrors many times - kids getting the scoot, a drunk knocked it over, I laid my scoot down in sand on my own street.
Misc small issues, replaced belt early at 10K, upgraded roller weights to dr pulley. Panel light goes on/off and is off most of the time. Gas cap had problems opening and had to adjust the tension screw under the fairing. oiled all cables, perfect ever since.
Anything, cable, lock, ign etc that needs attention, clean, lube, adjust, gets it, oil chg ever 1200 mi. Costco gas - premium, new interstate battery last year.