I studied at UNSW which was awesome! Here's what I found.
I think you should definitely live on campus! The campus is close to bus stops that can take you to the city and different beaches, and you'll meet tons of people. I applied for The Kensington Colleges but was too late and got a later preference, soI lived in UNSW Hall and loved it. It worked out for me because with UNSW Hall you still get to live in a dorm (with a single room, communal bath, 7 days breakfast and dinner), but we don't have as many activities as Kensington does so we're more free to go explore the city/try different bars and clubs and all that. BUT that being said TKC is a lot of fun and they have loads of events and it's almost more like a fraternity style partying and all that. There's two other dorm style places that I know a lot of exchanges live in and that's Columbo (you would have to cook your own food) and Fig Tree (which is a dry dorm). Some people also live in apartments called the Terraces. I know the people who lived there came with a few friends and I think since you're kinda isolated in your apartment you don't meet as many people.
If you want to live off campus a good place to start is flatmates.com.au. Some people lived in Airbnbs or hostels until they found roommates. There are share houses near campus but I'm not sure how people found those.
If you're lucky enough to be able to take a bunch of free electives then do it! You definitely won't want to be spending a lot of time stressing over classes. I took Business Finance, Entrepreneurship, Intermediate Macro, and Accounting 1. All had finals and periodic tests. There's a good amount of classes that do papers instead of tests. This is really cool because it means you have a whole month during exams where you'll be free to travel, so I recommend taking advantage of that!
It's easiest and cheapest to eat in your dorm on campus. My dorm didn't provide lunch, so I basically lived off of Boost smoothies. There's a Coles and Woolworths (both are grocery stores) near campus and an IGA convenience store on campus. On upper campus there's a really good salad place called Stockmarket. The cheapest coffee on campus is from the coffee cart in the main quad by the library.