As to a paid ticket, it's fine as long as the SGN segment is okay. There is a special rule applicable to Vietnam and I dont recall if it applies to SGN, HAN, both, or neither.

As to an award ticket, what you need to do is to add up the mileage of the segments and decide on a class. Your trip as written is probably not valid for two reasons. First, it's about 35,898 miles and the max is 35,000. You would have to break it up into two trips or cut off a segment to get it below 35,000. Second, you are limited on QF to five stopovers max on a oneworld award. It seems from your routing that you want to stop in at least six places (DXB, SYD, SGN, LAS, MEX, MBJ) and maybe more.