Visiting the US from Australia - Car insurance/rego etc
I have done a fair amount of traveling with cars, buying cars and associated admistrivia in about 5 different countries all over the world. I can relate a few of the generalities that might give you some ideas, but no real specific guidance.
The main issue for you is insurance. You can't get it here, simple as that. You need to have an active policy in Australia that will cover you overseas and allow you to add a vehicle to it by telephone call after you buy it here. There are a few insurance carriers that cater to military personnel who need to do this sort of thing which I have used in the past. I'd be surprised of they didn't exist in Australia as well, but don't know. It will be expensive at your age, but that's just the way it goes.
Your driver's license will be good here, typically for up to 30 days in most states, as long as you can show an arrival date by some sort of travel document. This varies by state. The only requiremnets you would run into are regarding the resident issues, which don't apply to you, unless you overstay. Not planning an illegal immigration are we? :axe:
Registration should be fairly straightforward if you buy from a dealer. They should be able to provide 30 day temporary tags. At least they could probably get you a transit or shipping registration that would be good for anywhere from 10 to 30 days.
How long you planning on staying?
HTH