You can do initial checkin online, but still need to have your passport data page <<< line dipped into check in counter computer and get an Expresspath card, so will need to be at airport premium check in queue.
Shouldnt be too long though, maybe 3.5 hours before a flight, half an hour in checkin queue, and the rest to get through outgoing immigration, and then int security screening.
Take all things out of your pockets, even passport in overhead bin bag, as you have to do a mock surrender, if the "guards" pick you to have a full body scan done to you.
Expresspath card can shorten time in immi queue, and int security queue.
I have done SYDi departures many times, and have always been put aside to the full body scan. They even have the gall to ask me to take off my no metal in it shoes!
It will be a learning experience.
Because MELi is not a 24 hour prior check in, its no use being at the airport too early for your flight.
Your passport will need to be dipped into their computer, QFs one, even if you have done OLCI and have your API details in their system, o, and also you need to get an OPC, these are available to fill in before you get to immi line.
Fill it in, put it with your BP into passport data page, go through int security, then passport control, then lounge.
F is great to plan for, Jessica said that the MELi QF lounge not as good as F lounge, but you will get to see F next time anyway. I am doing QF F lounge probably in Dec this year, my first and probably last!
Edit: witin MMB, there is a spot called "enter APIS". You can do that now if you havent done so. Still need to go to counter though for other procedures.