Pretty easy, as it was so quiet.
Border Force agents intervened before reaching check-in to verify our ability to leave Australia (this is where they check passport, then ask for exemption letter, if you have, and if not, call someone to check your immigration records to verify your entry/exits from the country would suggest you are not resident). The check (ability to leave the country) was repeated by checkin agents. The rest was the normal process - security then smart gate.
The longest part was waiting at checkin for them confirm if Bar Pulpo, airside, was open to use our vouchers (given vouchers in lieu of lounge access), as if not we would have to use them land side (one of their staff was heading airside to the gate just then, so they agreed to check).
The other tips
1) Very little F&B airside. In MEL, Bar Pulpo was open, but only had drinks and overpriced chips/chocolate bars available as was shortly closing, so we spent our vouchers all at once on 2 drinks each.
2) Don't be a lemming! We noticed almost the entire flight sitting at the gate the flight was departing from (~100 people). This was particularly important leaving Melbourne when the city was recording up to 700 cases a day. Unless clinically deaf, difficult to miss announcements, even being 100m away at an empty seating area, as it was the only flight departing. I guess the thinking is that everyone is getting onto the same plane anyway, but the aircon on the plane is such that spread is likely to be restricted to a few rows around where sitting. Needless to say, we sat well away from the gate in a gate full of empty seats (I do that at the best of times, I hate being in crowds if I don't have to be