I do not know where you're flying out of to get back to SBA but considering you have seven days, I would fly into Melbourne, spending a day (or two if you're so inclined). I think Melbourne is a great city, different to Sydney but I only really know the city relative to sporting events I've been to at the same time. Then catch the Spirit of Tasmania (a ferry) to Tasmania (Devonport), traveling anti-clockwise visiting Hobart, Port Arthur and making your way to Launceston where you can fly back to the major city you are departing from.