If considering PT in Sydney, I would install the TripView app, and add whatever routes are relevant to your travel. The paid version isn’t much (it was in the order of $5 when I bought it - but that was loooong ago) & I think the only difference with the free version is that it only stores 5 routes or 10 routes or something like that.
You can save the 400 bus from domestic to international, and the train from domestic to international, then when you’ve picked your bag up you check the app to see which option’s going to be most suitable. It uses the public API’s published by the transport authorities to keep location & arrival-time of buses & trains & ferries up to date, within about 30 seconds or so, so if your ride is late or early you know about it.