Thanks for creating this module! I was halfway through creating an Australia Post module for Commerce when I stumbled on this.
One thing I noticed is that when the services are saved initially they are not available because the commerce shipping services are cached or the rules cache doesn't know about them. I created a patch that resets these caches when the commerce_australia_post_settings_form is submitted. Similar to the commerce_ups module.
I also added some validation to the height, length, and weight fields.
I've attached a path if you want to incorporate these changes.