The itinerary looks OK.
Stopovers are only relevant in the continent of origin, so your comments about HKG and LHR don't matter.
Yes HNL-SYD is 2-class.
Going back to SYD is fine, but remember you are only allowed stopovers at two out of MEL, AYQ, PER, SYD.
You have already used the 4 segments in SW Pacific so you cannot add AKL (cannot purchase extra segments in the continent of origin).
The only place you can add an extra segment for free is in N America.