Definitely drop the US. Hong Kong and Bangkok (assuming the political situation is stable) are great. No need to include Singapore if going to Hong Kong, IMO. It would be a shame to go to Australia without experiencing the Outback. I think Broome and the Red Centre are brilliant. I've spent a ton of time in Oz camping and 4 wheel driving the bush. Not for everyone, for sure, but if you want to experience what makes Australia different, the Outback is the place to go. Not Sydney. Not Melbourne.