The minimum connecting time is 1.5 hours on a through ticket; being separate tickets I would extend this and allow 2 to 2.5 hours . If booked in J on QF domestic, then if you are there in time for an earlier flight then , as long as it isn't full, you can hop on an earlier one, so no real need to worry about having to sit around too long at the Blounge

There are showers at the business lounge

Dave