You do need to be careful how you split brisbane up with new teams. There is not the population or "sprawl" or tribalism the way you have it in Sydney. I know, I have lived both places and still do a lot in Sydney. They are very different and in some ways not obviously so.
I think a Western Corridor/Ipswich team is a much better idea than another otherwise undistinguished "Brisbane" team. They have the population and sense of self, as being separate to Brisbane, the right demographics and would be motivated supporters at all levels (fans, business and local government). Its LIKE a second Brisbane team, but not. Like Paramatta is a Sydney team, but not. Sort of. They have a great champion in Steven Johnson too. After that I would look to the Sunshine Coast for the same reasons. THEN drop a second team into Brisbane proper, or even look to Logan City instead. South East Queensland is all within an hours drive of Brisbane, but by not dropping a team right on top of the Bronco's you seed new areas and give the Bronco's supporters new external but still local enemies to fire them up.