Just MHO:
Not knowing what Melbourne temperatures are like, I'll have to share my experiences and you'll have to figure out what to do for your situation. I'm going to get wet if I'm riding in the rain. It'll be from the rain without a jacket, and sweat if I've got a jacket on. About 20C and above, forget about the jacket; below 15C, put up with the sweat to stay warm. In between, flip a coin. I settled long ago on a Showers Pass Transit jacket; the two way zipper and pit zips allow me some adjustability. Stop by your local bike shop and see what they've got.
Also FWIW, fancy breathable jackets work best for me below about 5C. Above that my sweat overwhelms the breathabilty aspect.
The biggest factor on bike maintenance is to wipe down the chain after a day's ride in the rain, let it dry, and apply and wipe before the next day's ride. Use oil (aka wet lube). If you forget the next day, the residual oil will provide some rust prevention. IME a good rainy ride with dry lube will start rusting the chain within a couple days unless you put some oil on as soon as it dries.
Two more things. Once a week or so wipe your rims clean with a paper towel or not-oily rag. It's amazing how much gunk accumulates on the braking surface when the roads are wet. Also you'll want to increase the frequency of lubing pivots on your brakes and derailers, and see if you can get a little oil into the working parts of your shifters/levers.