These boxes are not retailed by Australia Post as they have no value.
Some Post Offices will give you a box if you are a regular customer who sends a high volume of parcels and pays for the post over the counter.
Tracking is included as part of the regular cost for domestic parcels. The post office puts these stickers on a parcel to provide that service when you lodge and pay the parcel post cost.
My advice is to read to the listing as many of the questions you ask are answered in the listing description.
"The label does not include any postage value, so stamps or postage are still required
The label are used for parcels, not for letter delivery"
