There's no arrivals lounge facility at Sydney.
You can either treck across to the domestic terminal (effectively a separate airport on the other side of the airfield) where you can access the QF lounges. You're able to go airside there without an onward boarding pass. You'll need to retain your F boarding pass to SYD for lounge access under one world rules. I know there are transit busses to domestic but not sure if you need to show your onward reservation. The alternative rail link is expensive for the short journey. Otherwise, if this does not appeal there is a Rydges Hotel immediately opposite the International Terminal where you can book a day room. The day room rates are usually pretty reasonable. The treck over to domestic IMO really isn't worth the hassle unless you really need to go there. I'd be looking at the hotel day room as the most comfortable option.