I know less about diplomas than anyone here, but to keep those options open you'll just need to make sure you take Biology in both second and first semester and also Chemistry 1 and Chemistry 2, presuming you have done Chemistry in VCE. If not, you'll need to take Fundamentals in first semester, Chemistry 1 in second semester and Chemistry 2 over summer semester to catch up. Then you'll have two subject slots free per semester - you can take another Biology (flora and fauna, so not really medical related), Psychology, Physics and a few other things as electives in first year (one in each semester to leave room for breadth). That's all you need to decide on for the Science part for now - it might seem appealing to start planning the next three years over all, but I would recommend just doing your first year and taking it from there. Uni is different to high school, you might find you're attracted to different things and start figuring some stuff out. Those subjects leave all of the majors you mentioned open from a first year standpoint.
I'm less sure about the Chinese subjects meshing in with the breadth subjects, and when you have to start studying it (eg before the diploma or not), so let's let someone else work on that part.