Hey, congrats on getting into Unimelb! I'm not an expert at this either since I'm not planning to go into Med, however some of my friends are planning the same pathway you are (who are going into second year now). The only way for you to do Biochemistry is if you do the Fundamentals of Chemistry (Sem 1) --> Chemistry 1 (Sem 2) --> Chemistry 2 (summer) pathway unfortunately, but if you're adamant to study Medicine then you must do this.
Physics might also be complementary, where some of my friends did Physics 1 (Fundamentals or the normal one, depending if you studied Physics at high school or not) and then continue on with Physics 2: Life Sciences & Environment, which is very relevant to medicine/area of interest. My friend did this subject (also studying science) and she said that a lot of the students were mostly biomed kids in that subject! Note that Physics 1 (Fundamentals or normal stream) is a prerequisite.
Also, completing Data Analysis 1 (MAST10010) will be very useful as this subject (only prereq is Maths Methods, study score of > 25) is rather complementary to the Biomed-only subject 'MAST10011 Experimental Design and Data Analysis'. Don't worry too much about second year at the moment, doing Bio and Chem subjects as pre-reqs are sufficient but keep your options open (physics and some maths will be useful). Good luck with it all!