If you're confident in Maths I suggest doing Further or etc. now if you can, to give yourself more pathways. If you're sure you don't need it as Prereq that's fine. You can always fulfil a certain requirement through a bridging course or do the single VCE Maths subject at RMIT (which I currently would recommend if you can, cos Maths bridging courses and their exams are commonly completed in a month, at least VCE subjects are slightly less compact).
+ Always remember, don't let anyone depict what ATAR you get. Aim as high as you want. Of course, don't stress if you don't get straight As or A+s, learn from your mistake. Just make sure you do the best you possibly can (as in don't predict or assume that you have a limit, you don't, it's just that some need to work harder or less to reach a certain target).
Happy days