Thanks percysmith. Since the total miles will be just over 36,500 miles that will 240,000 AM needed for an MCA which will be the best way to book this trip. Can I ask about the best way to book this. To start a booking like you have suggested do you do it online or call up at this first stage? I realise that after the first flights I will have to call up to add other flights. If I follow your suggestion to book initial flights it may work to book SYD-LHR with JL and wait to add LHR-EZE later, since those flights still seem to be available several weeks later. Once I have JL and BA in the itinerary that gives me two One World airlines for the MCA. Looking at award flights released for SYD-LHR in J over the last few days they are going very quickly so I want to book the first flight as soon as it is available.

In your suggestion of ZRH-(BA)xLHR-(CX)xHKG-(CX)SYD//(QF)CBR-SYD at the end if the trip - what is the purpose of the //(QF)CBR-SYD after arrival back in SYD? I can see why you suggested to add it at the beginning when you said "That's already a oneworld award" and then remove it when adding further flights, so if you were using CX and BA you needed another OW airline to make it an MCA. If I start off with JL and then BA that gives me two OW airlines.