I suggest you get your FAA ATP then convert to CASA ATPL. otherwise you must sit all cpl exams and WILL take forever. Get you FAA ATP then come over sit the casa CPL law, IREX anf then ATPL Law in that order then do a couple flights in twin doing approaches and then do your ME CIR flight test.
However i suggest you do a ground school for the IREX because its 1000 times harder then the FAA instrument exam.
Do it that way if you can hold out instructing till you hit 1500TT in the US!