Ring your local RTA branch....
It will take a long time to get a comprehensive answer....
Generally, in most states you 'can' FIT them without an engineers cert however you WILL need one if you plan to FILL them with tyres as they wont allow the track increase.[}:)] Of course there are always exceptions and it depends on how you fit them... Some rego guys wont like them, particularly when combined with a tubbed rear etc.
Insurance is a funny one. Depends on who you talk to and what the different insurance companies class them as, wheel flares or guards lips (think 4wd) or replacement fiberglass panels. (think kitcar)
Two very different categories.....[x2x]
Shaun