Ahh you ask some complex questions and we could probably have a 45 minute convo about each. Ill try to answer them with some hindsight and not bog you down in too much information.
1) When you come here, you will get to know the city and public transportation, where your clinical school is etc etc and you will almost certainly move after your first year. Everybody I know is moving after first year and you will meet plenty of mates to move in with. It's impossible to figure out properly where you want to until your here for a bit because there are so many factors. Newtown is the safest bet in terms of closeness to the train, uni, most other students, and plenty of stuff to do. I recommend you just find a place in Newtown for the first year (maybe Sydney uni village) and then figure out where your going after. Bachelor places in Newtown run around 350.
2) I'm first year so I have no idea. I know I probably won't do it because it delays graduation until the subsequent year and, thus, internship is also delayed.
3) I'm not sure of the exact internship numbers..... check the HETI twitter page for updates as well as AMSA. The government is saying everyone who wants one got one but AMSA is saying this is not the case. The senate recently voted to guarantee IMG's internships so we will se where this goes.
4) Go to the registry and get a letter from them saying how long you have been licensed. Getting a license here will make getting into bars much less of a hassle. Aussie bouncers all have a long thick metal rod shoved far farrr up their ass and will randomly give you flack over you Canadian/US license not being valid.... it will ruin your night many times over. Also don't skimp on extra baggage. Everything in Australia is more expensive and it will very likely be cheaper to bring it here than to buy it here. When you arrive, just take a cab home and don't bother trying to figure out the train because its not that much cheaper (airport train tickets are ridiculously expensive) and a huge hassle with all your luggage.