Dont know what airline will put you directly into the LHS of an airliner with just a piston GA background?
There are actually quite a few instructors moving straight into airlines without charter/rpt experience.
Have to agree that Singapore Flying College is probably the best option that fits your requirements.
Pay on salary and good flying hours.
Living in Perth is not cheap but a good place to live.
If your flying school is screaming for instructors then ask them for their pay and conditions, if they are that desperate they'll pay for your training otherwise its just talk.
It will take a minimum of 18months to get a grade 1 (which is what the industry is short of) and you will have to get 50hrs PIC/ICUS on a twin to teach on multi engine types(multi engine training approval). All in all this may take 2+years.
The only reason to do charter is that you may get airline entry requirements a little earlier.
Whether you are better trained/prepared as a charter pilot or instructor will depend on who trains you and how the operator goes about their business.