Hi, to fly an Australian registered aircraft you must have a CASA licence - CPL or ATPL if flying for money. I can't help you with visa types - that's a whole new horrible convoluted field.
Converting to a CASA CPL is not too bad - see the CASA website. (As a CPL you're expected to find this stuff for yourself, not ask your CP for every detail.) Converting to a CASA ATPL is much more expensive and requires a multi-crew flight test in an expensive aircraft. An ATPL is really nice to have but only required for captain of a multi-crew aircraft, not for most single pilot ops.
Almost nobody in Australia sponsors international pilots - there's plenty of locals desperate for work - so your best bet would be to convert to a CASA CPL yourself and then go looking for work.