How do I ride one in Australia without getting run over?

Well, can't tell you anything specific as I have not been there.

Usual tips that from what I read online hold true in culturally western traffic systems is be visible, take your space, ride like absolutely everyone is actively trying to kill you. I know the latter gets thrown about by car drivers constantly but it holds much, much more true when you don't have the metal cage around yourself. Check what any car you can see is doing, blinkers are obvious but can be deceitful, look for the position of the front wheels to tell you where people are going to go. You have great visibility on a bike compared to a car, use it to your advantage.

Also never, ever be next to a lorry. Brake or accelerate if you can, if you're at a stoplight and one pulls up next to you, move back or fucking sprint it out of there on the green. The side of a lorry is the death zone for cyclists.

Take your space and be visible is basically intermingled with each other. I mean, make sure you can be seen, use lights in non-perfect weather (even if it's just a bit grey out), fit some reflectors to your bike for all directions and maybe your backpack or jacket or helmet, but this whole "invisible cyclist thing unless they're riding around in a full neon yellow bodysuit" is a myth perpetuated by car based societys on why they keep killing cyclists. Nobody ever has trouble seeing a black car, somehow. I hate to be advertising, but Fischer makes what's called a 360°-Degree rear light. In addition to a rear facing light it projects a red circle downwards. This makes cars pass less closely from my experience, I guess the whole red light = no go area is deeply embedded enough in peoples brains that they subconsciously avoid it even in this case.

The more important part basically is to take your space in the lane to stop people from trying to squeeze their SUV past you in the same one and cllpping you with the sideview mirror, so ride more to the middle. Seeing that that's verboten pretty much everywhere as far as I can tell, use a slight offset to the left (in your case).

Riding more in the middle usually means people actually have to use another lane to overtake you as few are psychotic enough to just straight up ram you off the road and no matter where you ride you're gonna lose that one. If they then pass way too closely, you at least have space to your left to evade quickly instead of either eating shit on the curb or just straight up driving into whatever is on the roadside or getting squashed.

Basically, if you're expected to ride with cars, act like one.

Also you'll be seen better. Car drivers are conditioned to think in one lane = one vehicle so they look for them in the middle. This hoids true at intersections, too, they're not going to look for anything in the edge of the lane, if they look at all.

People will probably honk or hurl abuse at you occasionally for it because they're shit and have huffed too much exhaust, but being yelled at means you're being noticed. Don't fall into the trap of trying to be the considerate cyclist by fulfilling some unreachable ideal made up by car drivers, it will not work in any way and you'll put yourself in more danger. I'm not saying be a dick, allthough I'm not going to stop you if you want to go full U-Lock Justice, just don't compromise your safety to be "considerate".

Be very fucking careful coming into any intersection at speed from any position that is not the road, such as a bike path or the sidewalk. Car drivers do NOT expect any object to appear from there quickly so they don't even check for it.

Always keep enough distance to parked cars that some moron opening the door without checking does not hit you with it. It's the equivalent of hitting a wall head on. This holds true for both sides of a parked car, probably more for the passenger side as you should stick to the middle anyways if you're on the road.

For intersections especially, if conditions allow it's always a good idea to use your lane in a way that means you have the maximum amount of angle to check / be seen by the crossing road.

You also have a fairly high position on a bicycle compared to at least normal cars. I often stand up before intersections to check whether a car is coming by looking over things, usually parked cars.

Also how do I keep a bike in good condition?

I've compiled some beginners tips in this post.

Depending your standard, that won't keep a bike in "good" condition necessarily. You'll have to adjust the brakes and the shifter occasionally, too and obviously you'll also eventually need to replace parts. Look up how to adjust your brakes and your shifter and you're probably on a good way to keeping your bike in a good condition. You could always tinker with it more to eek out 2 more Watts or whatever, but that's more of a hobby than an actual necessity at that point.