Are you sure that the BA scheme is the best choice of schemes? Neing in UK doesn't mean that BA is necessarily the best scheme. Depending on your routes, class of service and where you want to redeem travel to , another scheme may be better
Can easily believe that there would be a better choice than using QF when there ( or even still when back in Australia )
If you have status from another scheme, you would be able to get lounge access by showing the card - getting additional baggage would require speaking to someone
You would likely be better to put the other scheme number in booking and be able to get seat selection as per OW statius ; you would get baggage allowance and lounge access as per card - then change the number at the lounge so as to credit to the QF scheme if you wish to do so