I'm in Year 11 right now, and it's like Term 1 so I feel like if I really really wanted to I could definitely get in. I'm doing Ext 1, and for the first test I got a high B - but it is just the first test so I don't really know. I genuinely like math, I think it is an interesting subject when I can understand it (which I do for the most part). I also do like a good 4 hours of math tutoring every week, but I have a bad habit of falling behind on school homework which is bad since the school homework is starting to get harder. I also feel like my algebra isn't like completely solid and there are holes in my foundation, but I feel like I owe it to everyone to get in, including myself since I have worked so hard for this.
If it makes you feel any better: in the grand scheme of things, it will make no difference. If you do well in ADV or EX1 or EX2, you will be regarded as being "kid that is good at basic math" from a university lecturer perspective (as these courses are all quite simple from a university math perspective).
If you are looking to apply for a very high ATAR program or a degree program which is highly quantitative, you should probably do EX2 (and do it damn well) as the others in your course will have done so, and the quantitative degrees will work fairly quickly through the first year content (at a high ranking university, you need to be getting distinctions to justify being there, so starting your courses strong is helpful).
Every year I teach students in prep math + Math1110/Math1010/Math1131/Math1141 across various unis, as well as a mix of second- and third-year linear algebra and ODES + PDES + graduate DEs (teach grad DEs rarely), and the students who tend to do quite well in the first-year courses are the ones who come into the courses very strong, doing well in EX1/EX2 tends to be a mark of good performance.
This is because courses like Math1110/Math1131 are in part repetitions and in part continuations (if you do well) of the content which stopped in EX1/EX2. UON will not allow you to enroll in MATH1110 without at minimum a band 5 in Advanced, and UNSW is usually hesitant to let you enroll in MATH1131/MATH1141 without a cumulative mark of 100 in ADV+EX1. So, whatever one you choose, just make sure you do well if you want the highest probability of success in continued math courses (if they are required for your degree).