T1 LST - MEL, on arr into T1, its an easy walk.
But T3 to T1 SYD can be a pain the (p)um, as your timing is quite tight.
Even on the same PNR, the 6 alpha numeric code.
Having shown your passport at LST airport, is good, so you don't have to do it again to QF staff at MEL/SYD, but the SYD connection time is quite short, not saying it can't be done, but its tight.
I live in ADL, so for any int destos, I have to go via the eastern states, or PER if I want to go to SIN again, with QF.
I try to give it at least 3.5 hours, for the T3 to T1, even on a linked PNR.
Number of times, my flight from ADL landed in SYD, just a bit before 5pm, and I had a 6.30pm flight to various cities (on different dates) to NZ, dep at 18.15/18.30, and it was a rush, even with the QF bus.
Was in J, but did not use the QF J lounge at T1, as by the time I got across, it was near boarding time, and the queue to the plane was already forming.
If the concert is a can't be missed, I would try to be in SYD T1 the night before, the Rydges is very good, pricey and expensive, but just a walk across the plaza.
===
Bypassing the SYD dom - int transfer, go via MEL would be my advice.