Shared vs independant accomodation is something you'll have to speak to your employer about. No one here can answer that for you.

Regarding your current salary, is that in AUD or USD?

And is the 3.5k figure before or after you account for the cost of accomodation and utilities?

Either way you'll have to consider the impact of the USD rising or falling against the AUD so that you can calculate how much money you'll be left with when you return. It's a gamble that you'll have to take.

Expenses are hard to judge. It will depend on your lifestyle how much you save. You could easily be saving 10,000 per month if you tried.