I have done it all myself in the past, but not for probably twenty-odd years now so things may have changed (but I doubt it).
As I recall it was an absolute PITA, I believe Australian Customs made me register as an importer before they would even speak to me, and there's a mountain of paperwork involved with both registering and with the imported goods themselves, and everything took forever!
I remember them sending out one form in the post, then I'd complete and return that, then they'd send another form, then I'd complete and return that, then they'd send an invoice, and I'd pay that, etc. etc., and a week or two between each go-around.
I'm pretty sure they stuffed me around for over a month, even after it had landed in Australia!
And that was without any quarantine considerations, if you're importing anything with any biologicals (including a wooden pallet, or roadkill stuck in a tyre tread, or mouse droppings, or any kind of insect infestation) or asbestos (or probably a long list of other things) then I'd reckon you could add at least another month or six weeks to the above.
So if you're in a hurry (or unless they've improved their procedure) it may be worth paying a broker to do it for you? Some freight companies used to handle all that side of things for you as well, as do Australia Post.
Is Jeff from Cali still around here somewhere?