A nice adavantage of being an expat is cheap money. Interest rates well under 2% from Asian and even Australian lenders.
Sadly, 75K Sing may not qualify you for re-financing of your Australian mortgage. The wage is considered too low.
On a bright note, you may be eligible for housing commission assistance from the Singapore government- or that is what Silkair told me once upon a time.
I thought the ex-Ansett guys who went to QF were preserving their Australian lifestyle on the most part. Why the big change now? Why give up the lifestyle for the worst paying jobs in Asia?
Taking your family overseas is a big, brave move. I suppose a QF seniority number allays any insecurities.