zdomerr,
1. You can get around Australia the same way you get around the US - planes, trains, automobiles! An example: Melbourne-Sydney by plane = 1hr 20min, Melbourne-Sydney by car = 10-12 hours
2. In the major capital cities, yes, the culture is diverse. All depends on what you'd like to experience!
3. Sydney weather: Google is your friend. Summed up: "Sydney’s climate is pleasantly moderate". From
here.
4. Sure, the people are friendly! But I find people are friendly just about everywhere, so maybe get a second opinion on that.
5. Australia is a lot like the US, in the sense that any Western nation is, but I have not been to America, so I can't give you any more specific info. I'm not sure what you mean exactly. Do you mean culturally, geographically, climate-wise?
In my searching, I found this website:
Study in Australia - I think it might answer a lot of your questions, but keep asking here if you need anything else!