I would ask here as the situation is similar to mine -

Flying CX 105 HKG-MEL, arriving 12:15pm, on an AS issued ticket.
Then flying QF 630 MEL-BNE, departing 15:40pm on a BA issued ticket.

Looks to me CX 105 arrives AFTER the morning flight bank of International Arrivals, according to MEL airport's Arrival information.

We can use Smartgate (HKSAR passport) also would have Express Path card (in CX business).

I believe we can do Online Check in on the QF flight 24 hours before departure, but we still need to do the bag drop due to QF's 7kg weight limit on the Cabin bags. We can do the carryon bags with our CX flight because business class has 10kg allowance. Normally ours are about 11kg we can juggle it a bit to make it work. So no checked bags on the CX flight, but need to check bag on the subsequent QF flight.

CX 105 seems to often have 10 to 20 min delays but it makes up the time on a 9hr flight. Barring a 1.5 hr delay recently, do you guys think the 3.5hr allowance is enough on the international to domestic connection?

Thanks a lot for your insights.

PS
QF630 seems to be a seasonal flight, only restarts on Nov 1st on each Thursday. Our date is Nov 8th. Looking at last year's data, it seems QF630 often has up to 30 min delay. Of course I should not count on that and in particular, we should do Online Check In once the check in open, when we are still in Hong Kong. Hopefully we can print the BPs from Online. Then we just need to drop bags.