Hey! As Aaron mentioned, you should definitely get a Working with Children check. Odds are you'll never need to produce it (I never have), but it's handy to have (and legally required, pretty sure). It is really easy to get too - Like, 10 minutes online then a trip to your nearest RMS (or whatever the equivalent is in VIC, wherever you go for your Driving Tests probably). Plus super cheap; not a huge endeavour to have one, and it will last all the way through university.
Beyond that, you
could look at paying for certification from the Australian Tutoring Association, but it's expensive, and it doesn't really add anything to your service. Definitely not mandatory, and I haven't done it myself
With regard to ABN as a sole trader; you are making money off of it, so I'd imagine it would technically need to be declared to the ATO. The tax-free threshold is reasonably high, so unless you are taking like 20 students per week, you are unlikely to ever have to pay a cent. If you aren't making much from it and have another job, you might even be able to declare it as additional income along with your primary source of income. Not sure of specifics, best to consult the ATO website and have a bit of a read, because I'm definitely not an expert!
For price, while I think what has been suggested above sounds pretty good, do some searching and see what other tutors are offering and what prices they charge! Also don't be afraid to change your price if you need to; it is all about supply and demand. If you charge too much, you will have trouble finding students. If that happens, drop your price! It might even work in reverse, who knows