If I apply for courses at Sydney uni through UAC and uni of melbourne through QTAC can I get one offer from each or only one? And if only one, how do you say which is your overall first preference?
They are separate so you will get one offer per "admissions centre" you apply to. (One each for UAC, QTAC, VTAC, SATAC, etc)
And there's no need to specify an overall first preference.
Yes you can get more than one offer, because you get your top eligible preference through the relevant TAC. So I could apply and get six offers if I did each system.
I got both a UAC offer (Usyd) and a VTAC offer (UMELB) and then just accepted one and declined the other in January.