Been reading along...
Just want to add a few lines if I may. If you are aiming for 500km in a day, it will depend what routes one chooses and how busy the roads are from all the myriad of road users, because if one is on anything other than a solitary mountain track, or a Gaosugonglu - expressway, then be prepared for any eventuality, and possibly either not attaining 500km but considerably less, or riding will past sunset. Some aren't comfortable riding at night, and I might agree if it were early say from sunset to 3-4 hours past, but after that usually the roads vacate of most of the 'other types of road users' and settles into a rhythm of taxis, buses, trucks... and the latter are usually more often the vehicle types seen most commonly when it gets really late, especially midnight and beyond. For me this is when roads become more navigable. But not everyone agrees.
My point is, plan for 500km in a day but work towards 300km as an average, unless you can jump on the gaosugonglu.
Make yourself a cheat-sheet, with all kinds of Chinese words (pinying) and characters that you can show to someone when you need assistance, whether it be food, accommodation or even motorcycle parts. Will make your life easier and as suggested a contact that can be reached any time who can help you explain something. The biggest issue with this though is that persons ability to understand and explain a wide range of things (not easy really as it sounds).
There's a list of bike part names in CHS - English here on MCM...
A small Lonely planet phrase book also can be very helpful...
Carry your DL, passport and copies of these...
Banking ATM cards... cash... and keep your wits about you... especially riding. Smile a lot...
Don't sweat the small stuff...
Carry basic toolkit, spanners, Allen keys, screw drivers, puncture repair kit and depending if your bikes tyres are tubeless or not will dictate what you need in the event of a puncture etc.
A simple first aid kit ensemble can be useful...
Zip ties, and some gorilla or duct/duck, electrical tape and some wire...
I could go on, but been plenty of suggestions already.
Shiny side up, rubber side down