How long do you plan to stay in Australia?
4 years students visa?
4 years as a sponsored employee visa?
PR?
How often do you plan to go back to the US?
Not that I can help withe the answers, but maybe if you provide the info, it might help the others.
Personally, as an Australian citizen, I am with both QF and VA, have been with QF since 1997 when I was an Australian PR visa holder. Been with VA for 10 years, 2005.
I certainly would not go and join SQ/MH's programs.
Points life do die with airlines, so if you do plan to go back to the US once a year, maybe still fly AA codeshare with QF, but maybe start your flying life downunder with QF.
300 SC for PS is probably a large number to meet. A few local J class flights will get you there, though SG harder still at 700 SC.
If no regular flying, but when you do fly occasionally, paying your own $ and flying J might help.