Glad I can be helpful! (At least one more post will be coming...)

I've heard Australian Post offices have all kinds of shopping and stuff? Like they're a one-stop errand-running shop?

Well, you can certainly buy stamps and packages there. And you can pay your bills there (I used to pay all my household bills at the Post Office, before I switched to online banking). And they usually have lots of little random things that... kinda don't fit into a specific category. You'll see. :)

There are adaptors sold in Australia, but if you can find one before you'll leave, you'll at least know you've got one! If not, I'll help you track down one here...

I've heard a lot of vague things about extra bills/fees on top of rent, particularly related to water? And that they can be extremely high?

I pay:
- rent
- water
- internet
- electricity
- gas
- mobile phone (don't have a home phone anymore)

The middle three (water, internet, electricity, gas) will each cost me around $100 every three months.

I'm not aware of any other bills being standard in rental properties.