You can actually teach with less than 8th grade. However, you won't be able to charge as much as someone who has a formal qualification - probably only about $20 an hour (many teachers charge more than that for half an hour). Obviously, going on to do your A mus and L mus would be a huge advantage, and I believe there's an AMEB teacher's qualification that you can get, which means your students can do AMEB exams (could have that a bit wrong, though).