Definitely sign up to MyPost and print direct from Australia post rather then eBay, as curraone said you get discounts the more you buy.

But you can also import the eBay orders to the website, generate and print your labels,   and once paid for it uploads the tracking details back to eBay,  so you have no need to upload tracking, etc.

If you have a friendly Post Office, they will register your Mypost account to their account, and you get an immediate 3 months on Band 3 discounts.  Well that was true about 12 months ago, but check it out.