Go and see an accountant for sure, but ask your muso mates if any of them know a good guy in your state. I use a guy in Adelaide at MTS. I didn't need an abn or any hard "proof" of my income from music. Just reciepts of what was spent and in some cases I just told him what I spent or made; for example $7 a week on rehearsal room hire, $300 from a gig.
The cool thing is that you can run your band as a money losing exercise and claim everything against the tax on your primary job. I am also a uni student so I can't claim as much as when I worked full time (because I'm paying less tax now and getting Austudy), but next year when I go back into the real world I should be paying more tax and be able to claim more on the mesa gear.
I still can't believe we can do this, but take advantage of it before K-Rudd and the Swan find this hole in their budget and close it up. Hopefully it's too small and they don't notice it or are liberal enough to allow it to continue.