It is worth a trip over to the QF F lounge. You can sit down and order food. But after you eat, the lounge is pretty stark, so you might want to head back to T4.
Walking the connector, the QF F lounge is right there on the same floor as you exit the connector hall way. You can miss the QF F lounge if you don't look to the immediate right after you enter TBIT elevator area. When I was there last week, they were working on the escalator which takes you down one level on the TBIT side, but to go the QF F lounge as you enter TBIT - don't go down - just continue straight to the left and then when you turn right QF F is there.
The menu is good, but somewhat limited. The wines are good and there is full bar. But maybe a 1.5 hours before your flight head back to AC/Flagship lounge (if EXP).
I am not aware of any arrival lounges in SYD. If SYD is your final destination just take train to the area of your hotel. Only 15-20 minutes from airport to Downtown by ferry boats, Opera House area.
If you are connecting on a domestic flight, you take the bus between terminals after getting luggage and dropping it off at the transfer drop point. They have showers, etc. in the QF domestic lounge/business lounge. As a J passenger you can use the business lounge side but the showers fill up on that side so maybe start in the regular QF Club side first then move over later to the business lounge section.