On a whim, I just tried pricing it through AUS and it works -- AVL-AUS on Feb 5, AUS-
BKK on Feb 6, returning BKK-AVL later. Prices at $1825 and change using B and M classes. Some of the routings use CO equipment, so be careful about 50% EQM.
Just use multi-city and route AVL-AUS, AUS-BKK, BKK-AVL.

To answer #1, I think I'd try making that reservation online and putting it on hold -- that is an option when you get to the purchase ticket page. Just click hold and not buy, note the reservation number -- it won't have a PNR yet, I don't think, but there will be a number associated with it. Then call and see if they can ticket it for you. That used to work.

To answer #2, if you are on a flight that has the same number all the way through, for example NW1 MSP-LAX, LAX-NRT you might not get upgraded on the MSP-LAX leg even if seats are available because you will not be upgraded on the LAX-NRT leg. But, I don't think NW follows the practice of using the same flight numbers on the US extensions of international flights too often. Some other airlines, do.

Hope this helps. And think about posting something about your experiences when you return.

tom