well monash need you to take a bridign course if you dont do bio in yr 12. And nowhere in NSW do you have to do chem for medicine (i know in monash + UTAS you had to!)...my mate got 99.55 uai and got into UWS without chem..
Prety much most of people i know who got 97+ did 12 units- it wont affect you if u r dedicated enough!
in conclusion...physics has no benefits in applying to med although certainly helps with ur understanding of how the body moves etc. (but will be covered in every med course).