Ok, for .com.au you need an ABN, and it's *supposed* to somehow relate to your website name. If it's not it will be shut down eventually.
Personally I don't think the .au bit is *that* much of a blessing, it's only worthwhile if you specifically have a business you run through it. For example, Google knows that this site is Australian and reflects as much when you search for Aussie results on stuff - despite it only being a dot com registered in Germany in 2006.
The difference between the two you mentioned is basically nothing but the price. That's just the way it is with internet stuff, the best deal is the one that suits you on the day. Domain registration means nothing, any extra money spent is simply profit for the registrar - just like a number plate, it doesn't have any intrinsic value, only what is made of it.
That allshotsimaing.com place is just a pbase.com redirect. you can do the same or better at the sites I listed above, without needing any web design skills.
My recommendation is smugmug.com, I don't know the prices per year now, I think intro was $40, medium was $100, and pro was $150 (US). I took the Pro account, and that's what you see when you go to http://gallery.aussieexotics.com
I haven't updated it in almost a year because I spend so much time here, but the pro account there will allow you to sell digital downloads, portfolios, posters, mugs, mousepads, condoms... well, maybe not that, but almost anything based on your photos - it's just up to you to promote it. And once you pay for it I can have you up and running within a day or so.
Use coupon: F5CxHlOfM34o6 to save $5 bucks off the subscription fee.
Other stuff they do is you upload your original res photos and you can apply an automatic watermark to all photos - that's why on some of my older ones you see the multiple faint watermarks across them - I used to use them full on until I got too involved doing it all for myself. They have just recently started offering hi-def vids too, check the videos page for the latest stuff where I uploaded hi-def vids of the ferrari rally trackday. Plus all the stats on how many of your pics have been seen etc.