For BNE dom to int, there is no bussing around the terminal.
Its a straightish road, from the dom to int, very fast, more or less the same time as the Sydney T3 to T1.
The orange bus from BNE dom to int, is outside on the main road, you go out the BNE QFd terminal, you will see the BNE airport train station in the distance, about 500 m, that first road, you will see the QF crew, sometimes a lot of them, wait for an orange bus to come, it would say BNE int or Skygate.
At BNE int, it will go up the ramp, arr is on ground, dep is on one level up, you enter the terminal, and then take the escalators downstairs, don't ask me why, but as your passport has been dipped, / swiped on the airline side, you just need to go through outgoing Au immi, which is on ground level.
You then have int security screening, then go upstairs again, to the gates area.
Lounge time, if you have access.
QF dep from the far left hand sides, facing the runway.
I have flown out of BNE int once as a dom pax on int flight, (can't remember the QF flight number) when that 747 used to fly in from the US to BNE, then onto SYD, and BNE dom many times.
Edit, OP, which QFd are you on, 500/502 or the dreaded 504?