There is no interlining to JQ, but that is irrelevent really since if connecting from an international flight to a domestic flight in Australia , you need to collect baggage before clearing Customs. If travelling JQ, I think that you have to lug your bags to Terminal 2 for check in and cannot use the domestic baggage transfer desk in Terminal 1.

Rather than fly to OOL, I would suggest flying to BNE and then just hiring a car and driving the 1 hr to the Gold Coast or hopping on the train from BNE which will take you straight down there.

If taking a night flight from SIN, there is a non stop service straight to BNE (QF52 codeshare with BA7352/AY5896 ) departing at 21:20 arriving at 06:45. Much easier than flying SIN-SYD 19:55 arrive 6:10 and then departing at 08:30 arriving into OOL at 09:50 or departing SYD at 08:05 arriving into BNE at 09:30

If taking the civilised daytime flight from SIN-SYD , connecting to BNE will give a much easier connection and a more pleasant flight. OOL is still 20-30 minutes from the Gold Coast and , given the additional time needed to connect to JQ , will be no worse off going to BNE plus , if you have a through ticket in J, you will get business class on the QF flight

Dave