you can do what you have stated however with the recent enforcement/interpretation of the "two transfers" per city maximum rule you may not be able to transit HKG so many times.

But it really depends on where you ticket, which airline you use, and how good your travel agent is at getting them to overlook this rule.

Having said this you could fly directly to SYD from LAX and then go upto HKG and eliminate the first HKG stop. As for your second proposed itin - i'm not sure that QF offeres a MEL - JNB flight??

Your overall itin isnt so difficult so you shouldn't have problems rearranging it a bit to get to the places you want.