Not sure on the hard and fast but generally for .com.au yes you need an abn. As for hosting etc, crazy domains are where i buy domains as they are cheap. For hosting I use blue host .com again cheap ($6/month) but offers unlimited data, databases, email hosting and a range of other services like php, my SQL etc etc. So you can run Wordpress or joomla.
Oh and don't rule out the .co domains either no abn or other proof required. E.g.
www.astrophotography.co
Cheers