Need some help here please

Have asked for an upgrade from PY to J on a return flight from HKG-BCN. MP agent told me that the return is already confirmed, but the outbound is waitlisted. He also said that the ticketing would be held off until the 30th of June. My understanding is that this upgrade would 'cost' 30000 miles as a return.

If the waitlist is not becoming available at the time of ticketing the upgrade would be 20000 (as its one way).
In this case I would rather upgrade one way from BCN-HKG-PEK, instead of only to HKG of course. (ticket is PEK-HKG-BCN return).

Here is what I dont understand:

1. at what miles will the upgrade be charged? (miles required will change after 22nd of June, right!?)
2. what happens at the airport in HKG outbound, if there are seats in J, and I am still waitlisted? (but already ticketed on the return from BCN to HKG)
(2a. If I can get an upgrade at the airport, how would it be charged?!)
3. If I cannot get a seat in J at check-in in HKG, how can I ensure I am using the 20000 miles to get the upgrade from BCN-HKG-PEK instead of only BCN-HKG?
4. would it make sense to call MP again, and ask them to issue the upgrade before the 22nd (possibly avoiding higher millage requirements)?!

Sorry, but this is giving me quite a bit of headache, as different people tell me different things.

thanks