I have a HSBC account in the US but I mainly use it when I travel overseas in countries where their ATM is more plentiful. I also like being able to drop in a branch if I need to. It came in handy when I was in Tokyo... after visiting the royal palace, I really needed to use the toilet so I walked in the HSBC branch across the street and made a deposit

If HSBC says they can set up you in Australia and give you US accounts when you get here, I would definitely do that.