hold a valid and unrestricted license to practice medicine in the United States;
You may require the USMLE to be ECFMG certified for obtaining a valid and unrestricted license to practice medicine... though it might be possible to get contracts with specific hospitals or health networks. I do know of some situations where Canadian FPs have managed to go to the US without writing the USMLE and I imagine this process to be identical for Australians.
The US is a merit based system and has a large number of unfilled residencies every year. With a lot of hard work, good financial support, and the right motivation, you can match into some of the competitive residencies in the US from Australia. That being said, you have to be realistic with yourself. If you were not a strong student before, you will not likely change much while you are in Australia.
Skim the forum for the information you need and then ask specific questions as your develop them.
There is no need to stay in Australia for 4 years after you graduate to finish your GP training unless you want more clinical exposure and/or want to spend time down under. You will need to get permanent residency before you can even enter a training program. You would save yourself time and paperwork to just go back to the US and do your 3 years of family practice. You need to learn medicine under the US system so that you are able to navigate it on your own.
Residency is not just about medical knowledge - but even then - protocol differs from country to country.
I can't agree that the Australian GP training program is second to none as the scope of practice for GPs in Australia, Canada (FPs), and the US are slightly different and thus the training programs are as well. The training programs are also managed by different entities as well.
I would like to say that if one works hard and is in medicine for the 'right reasons', you will be able to learn what you need to for your patients.
One who needs hand-holding to learn medicine will make a poor doctor in the long term.