1) Most USyd courses are 6 credit points. A full-time load is 24 CP per semester, or 48 for a year. Medical Science requires you to complete 144 CP to graduate. There are several 3 CP units as well. Most first year maths subjects are 3 CP (you do two, plus three other full subjects).
2) Medical Science is fairly similar to BSc. First year you have to do 6 CP Biol, 12 CP Chem, 12 CP Maths, 12 CP Psychology and/or Physics, and 6 CP Molecular Biology. That's 48 CP -- your entire first year basically involves picking which biology to do and whether you want psychology or physics.
Second year has 36 CP of core subjects. These offer multi- and inter-disciplinary perspectives on bodily systems. They are Cellular Foundations, Nerve and Muscle, Cardiovascular and Respiratory, Microbes Infection and Immunity, Gut and Nutrient Metabolism, Hormones Kidney and Reproduction. Whereas most BSc students will do discipline-specific subjects (eg anatomy, pathology, pharmacology, immunology, etc), you will look at these systems from all perspectives. You'll learn the anatomy, histology, pathology, pharmacology, immunology, biochemistry, microbiology, etc that are relevant. It's a broader but slightly shallower experience. In addition to these 36 CP of compulsory units, you can do one 6 CP elective each semester. You can also do two electives, and postpone two of the core units (not cellular foundations however) until third year.
Basically it means that your options for majors remain open until third year. Which means you can pick what you want to specialise in much later, once you've actually got a good taste of everything. Third year medical science is the same as third year BSc unless you deferred one or two core units until third year (which limits your choices and I wouldn't recommend unless you really want to do a lot of second year electives, eg for a Psychology major).
3) Not especially easy. Depends what your skillset and experience is, though. As always, contacts are the most important thing and being an international student it's unlikely you'll have lots. There are resources to help you but if you come expecting work or relying on it to make enough money, you may have a problem.
4) Student accommodations are a great place to meet people. I wouldn't want to live in one beyond my first year at university. However, I know plenty of people who have and who have enjoyed themselves.
5) Pay attention to Molecular Biology (MBLG) in second semester, first year. Too many people hate it, or drop out in the first few weeks because it's super intimidating, but if you get your arse in gear and make sure you do well in it, it will make everything you do in second year much easier. Seriously, I cannot stress enough how important MBLG is to second year Medical Science. If you want to make second year Medical Science even easier, do Psychology, not Physics. If you want to make getting into Medicine easier, do Physics, not Psychology.