Welcome to Flyer Talk 20schwarz

1) Not easy avoiding HKG intra-asia or LHR intra-europe, especially for the places you want to visit. I you (re)ticket once JL joins then some different routing options open up within asia, but still would be 6 segments. The only way to get it down to 4 would be to purchase a separate ticket (eg BKK-HAN-SGN) - not sure if that will be cheaper or not than the surcharge (probably if you fly economy).

2) You need to ticket with an australian-based TA, or with a OW airline's australian ticket office. Up to the TA whether or not they are willing to mail tickets to you in SFO. If you want to reduce costs further you could buy it from AKL (rearrange the order AKL-SYD-BKK saving one asian sector and finish with SFO-SYD-AKL or SFO-LAX-AKL).