Hi Karl,
Have you had a look at
Used Cars - New Cars - Search New & Used Cars For Sale - carsales.com.au That is one of the most popular car sites over here.
You get car basic insurance with the car registration (rego) and then you can get other car insurance too.
Holden is common but it can also depend on what's around where you live. We live in a rural area and there are no European dealerships other than Mercedes. There is of course a big Holden dealership
Sorry I can't help you with the rest.
Regards,
Karen