Couple quick detail Qs:
If it's two separate itineraries aka XXX-ICN-PEK and PEK-HKG-YYY and the time in PEK is less than 72 hours, is this OK or does it have to be the same ticket number?

I know you're not allowed to go between cities, but can I land in PEK and go to the Great Wall/surrounding area or do I have to stay in the city proper?

Does it work if it's XXX-PEK-PVG-YYY within 72 hours?

I know PEK is on arrival at the airport, but is it as flawless at PVG, CAN, etc.