Some clarifications needed.

I will be flying into Beijing and then taking the train to UB. I know that I am not eligible for the 72 hour visa for this part of my trip.

I then return to Beijing by flight from UB and fly the next day (more than 24 hours later) to Sydney. This flight has a connecting stop in HKG but it is all the same flight number and I am flying through to Sydney. The way I read it though this stop in HKG precludes me being able to get a 72 hour free transit, even though I won't leave the airport in HKG. Could someone please clarify that.

If that is the case, I presume I will need to apply for a double entry permit as I am going: Sydney China-Mongolia (train)-Russia-Mongolia (bus)-China (plane)-Sydney (plane).

Also, what is meant by itinerary? (from Embassay website2) Information on the planned visit (arrival and departure dates, place(s) to be visited, etc.)

Do they mean the transport details, flights, trains etc and my accommodation details or do they mean this AND what I plan to do e.g. Sun 25 - visit Forbidden City; Mon 26- Great Wall at wherever I decide to visit it?
If they mean the latter, how specific do I need to be.

Apologies for what might seem stupid questions but I'd rather find out now than have an application declined or have trouble at the borders.
Thank You and Kind Regards.