Might be useful to take up physics, as it’s probably useful for other allied health health degrees like optom and radiography if med doesn’t work out.
Depends on your abilities but keep in mind that UCAT is very important. Doing a high scaling combination of subjects might give you a bit of a boost but making sure that you smash your UCAT is wayy more beneficial than a marginal ATAR increase.
And if you’re aspiring to do medicine, please apply to every university possible (within your means -i.e. don’t bother with Bond if your family can’t afford it). It’s actually kinda common for people to gun for UNSW/USyd med and refuse to apply for the “less prestigious” unis like WSU and UNE. If your heart is truly in medicine, then it doesn’t matter if you study at WSU/CSU/UNE/UoN or USyd, and it doesn’t matter that it’s called a BMed, MD, MBBS or MBChB (degree packaging and nomenclature mean nothing). It’s good to see that you have a big goal so go for it and good luck!