I read it as the OP is inquiring about the int-dom connection at SYD/MEL/PER or whereever the OP arrives first in Australia.

I also assume that the OP bought two tickets, 1 ticket Italy to AU and 1 domectic ticket. If all travel is on 1 ticket, there is no issue - you will be transferred to the next flight (free of charge) if you miss the connecting domestic AU flight (unless it is your own fault).

Anyway, you should be able to make that connection but be prepared for the worst case sceanario in case you miss the AU domestic flight = you have to buy a new ticket for the next flight. Luckily, domestic flights in AU are not that expensive - in general - so it should not lead to significant loss for you.

If you have travel insurance such extra costs should be covered under the travel insurance.

Good luck! - most likely you will make the connecting flight so don't worry too much.