Copyright is automatic without registration
worldwide (or at least with every country that has signed
the international copyright treaties - which is most of them). The US is the only major country I know of that doesn't fully honour this (while your work is theoretically "copyrighted" there, you can't actually enforce it unless you register that copyright).
You do not need to use the copyright symbol in connection with your work.
Copyright law is fairly standardised internationally. Obviously there are differences, but for the most part they're not substantial. The main differences are 1) Duration (it's excessively long in all countries though), and 2) The US's use of a registration system (I like that there is one - I wish we had one too - but I don't like what they've brought along with it).
The vast majority of what you read about copyright (e.g. what is and isn't protected, what you can do with it, etc.) applies whether you are in the UK, US, Australia, or just about anywhere else.
While you don't have to register your work, if you choose to (in order to make legal proceedings easier) then you can do so through the
US copyright office. This will most likely be accepted in an Australian court.
Personally I do not recommend using a "registration company". I think they prey on people's ignorance and fear. They're also only useful so long as the company stays afloat. Personally I recommend registration be done through a government office, or not at all.
Business names (and identities in general) are governed by trademark rather than copyright law. Registration is on a national basis, unless you apply for an international trademark (which can be done - separately and at greater expense).
But if you're "not so easily convinced and unsure" then why even ask in a forum? All we can do is provide the same answers you've already read and didn't like. If what you really need isn't answers, but rather just convincing, then go and read the sources yourself and draw your own conclusions:
Australian Copyright Council's Online Information Centre — Australian Copyright Council is a good starting point.
Copyright your Business and Designs in Australia? 
Can you also copyright your business name along with your artwork all in package? I am totally new to this and tips and advice would be greatly appreciated for those who have gone through it. 
Re: Copyright your Business and Designs in Australia? 
Re: Copyright your Business and Designs in Australia? 
