You've got more or less three options.
Entering with your own, foreign registered bike, which is possible but involves miles of red tape and a pile of cash. Most likely it will not work without "tour guide" and some unexpected charges may occur. It has been done many times and there are some agents to deal with. Consider minimum 3 months to get all necessary paperwork. One of these agents is Kashgar New Land Travel
Getting your bike into the country without an agent on the back of a truck or sitting it out at a border is very unlikely to work. If you make it in this way, you have to go out the same way.
Although it has been done before, it seems to be out of reach today.
The "get a bike in China" method is more feasible as long as you don't expect to get the bike of your dreams.
Legality of the rider is an issue and there have been many hot discussions about it already. As a visitor (except case One) it is very difficult to almost impossible to get your hands on a driving license. However, many people just bought a bike and rode all over the country without it and they were fine.
You don't need a permit to travel between provinces except for teebed and some sensitive places bordering it. Some regions are no-go for foreigners. On some inter-provincial routes you may run into check points.
All the above is based on this:
1 there are no rules
2 there are tons of rules to be followed
3 both, 1 and 2 can be simultaneously applied
4 different village - different rules
5 what worked yesterday, may not work today but may again tomorrow
to PM me if you are opting for Three