You don't need much maths for coding. If you are good at maths it indicates you could be good at coding. If you are good at coding, don't worry about maths - you have the bull by the horns.
What I did just there is discrete maths (If All dogs are animals, it does not imply all animals are...
Good chance - but don't get hung up on UNSW. Check out the satisfaction scores at QILT - UNSW and USYD scored below Wollongong, Newcastle, UWS and UTS. Once you have a job no one cares what Uni you went to.
Physics and (of course) Maths require good maths. Other sciences not so much. But don't think because you didn't get it at school you won't get it at uni (and vice versa). Hard work and determination are key.
Good chance as they let people in below the guaranteed entry. Don't bank on it though and have a back-up plan. Make sure you have an option you are 200% sure to get at the bottom of the list.
First, both are good universities. ANU has a better reputation internationally based on QS and Times ranking but also simply based on the fact that the name is more recognisable outside Aust. UNSW is very famous for some things in Physics too. Can you stay at home? Living outside home can cost...