Firstly, congrats on your ATAR and finishing school. Besides that, if you are looking towards UoM for graduate entry, you need to take 3 2nd year subjects (1 in anatomy, 1 in biochemistry, 1 in physiology) in order to apply for the MD program at Melbourne. These require you to take Chemistry 1 and 2, and Biology 1 and 2 in first year.
If you could tell me about which sort of engineering you'll most likely to major in, I could give you some more specific advice, but until then it'll be a tad hard because there are too many variables in the course plan to do so. The BSc program at Melbourne is extremely good in my opinion, giving me the option to dabble in commerce without committing to an entire Bachelor degree which I did not want to do. Breadth is an acquired taste but you have the option to do it at every university, just at Melbourne, it's mandatory to take at least 4 classes outside your home faculty.