For my money, the decision whether to have a store or not really depends on the volume of products and the listing strategy you want to employ.
This is a general link that will give you plenty of information on eBay's store options: Link hidden: Login to view
If you're looking for alternative sites to sell to an Australian market then you are limited really. Oztion and Trading Post are the two biggest local ones out side of eBay, but are still no where close in terms of traffic volume.
If you're finding good traffic and generating solid sales figurers through eBay, I would be suggesting taking a look at developing your own site and using eBay to generate traffic flow.
Never easy establishing your own site, but if you've made bronze on eBay, then it sounds to me like the potential is there.