3h5m is plenty of time for domestic to international at BNE, even on separate tickets. 2h20 on separate tickets is pushing it.

You'll have to get off the plane, collect your luggage (shouldn't be that slow compared to the US) then make your way across to the other terminal to check in for your VA flight -- not very far but not walkable. On separate tickets I think you'll have to shell out five bucks for the bus.

Of course the usual separate-ticket caveats about what happens if your first flight is delayed will apply. Catching a 6am flight is never fun, have you considered flying out the previous evening and spending the night in Brisbane?