Given that you are TATL and TPAC with AA, AA will likely ticket for you if you want them to. This has operational benefits when you go to use the EVIPs but may cost you some tax, though AA taxes on other carriers are minimal. And AA will need to pick up the ticket to update with the EVIPs. Not so with stickers or EXP upgrades domestically.

I would be very tempted to setup with the AA RTW desk with $$ ex Hanoi but to be paid for in Canada. A quick trip to Canada with payment at the AA desk at the airport. Others can correct my suggestion if better alternatives are available. Some may recommend a Canadian TA, but this would perhaps add the TA service fees. Might be cheaper to fly to YVR if AA has a desk there.

Routing I would seriously consider the WT+ upgrade CAI-LHR as this would give you 110% mileage and 150% EQP. Doing it LHR-CAI will add the very generous UK APD and I dislike paying taxes without obvious benefits. As well I would consider Malev on the BUD-LHR segment again for better earning. I flew them a couple of years ago without incident although it was a Biz award ticket. If BUD-LHR-HKG is a connection the Y+ alternative on QF is perhaps an option as the APD does not apply to connections. It would not be as important to me as the CAI segment as QF flights do attract status bonuses. Though depending on the day and flight loads, QF has been rather more generous recently as a result of overselling the Y cabin on longhaul flights. No guarantees. And the Y+ upgrades may not be within your budget.

I wouldn't worry about JAL before May and even then publicity will precede actions.

Changing dates on flight segments (after the first) is one of the reasons to use the AA RTW desk......

Happy wandering

Fred