Kristoff saidI like writing in my spare time, as a hobby.... But I was thinking, should I be aiming for maybe a published version of my work? I didn't do any English in school, so I'm all self taught. I feel like I have such great ideas, but no way to express them...
Well, you must have done SOME English in school, you're using it. You may not have focused on English, or taken extra courses, but surely the Australian schools you attended had basic English classes, yes?
That really could be enough to get you started. If your RJ profile is any indication you have a kind of stream-of-conciousness style, which some authors have used to good advantage. Although for better readability in certain circumstances and for conveying information you might consider the power of the paragraph break.
All you may need is to work with a good editor. His/her revisions could be adequate training for you, as you learn your craft by doing. That's how the American Mark Twain (Samuel Clemens) learned to write, in a natural colloquial style that made him one of the first superstar writers of his era. Instead of using textbook examples of good writing, you're learning from your own words and ideas, which will resonate better with you and have more immediate practical application.
Sometimes too much formal training can suffocate original talent, instead of showcasing it. I'm reminded of the Billy Crystal line from the comedy movie Throw Momma From The Train
, when he plays a teacher telling his students how best to become good writers: "Remember, a writer writes always."
You never stop writing, as the act of writing is itself a form of learning. It's a variant of the concept contained in an old vaudeville joke, when a man on the street stops another for directions:
"Excuse me, sir, can you tell me how to get to Carnegie Hall?"
"Practice, practice, practice."
So if you write in your spare time you're doing it right. And submitting for publication might get you some instructive editorial review. Or if you can't get that far, try to enlist the help of someone who has some editing skills, perhaps a teacher or professor you know. And keep writing regardless.