WorldRover,
Some of those questions i previously answered on Page 2, so go back and read my posts.
There is no per diem, but they give you an allowance which is around $1100/mo, so just call that per diem. You get free meals when eating at the layover hotels, other than that, you are on your own.
Duty limits per ICAO, but chinese do stretch some rules for the rest and what's not counted as duty, IE. Plane broke for 6 hours, then you need to sleep in the plane to ensure you get your rest before taking off again.
They do not do R/Ts to and from base. Read previous posts.