1. Yes, unless the car already has them
2. I don't think that child anchorages fit in the Supra (being a hatch and all). Find an Aussie delivered and go from there.
3. Yes - you need retractable seatbelts made to meet australian standards. I wouldn't try using secondhand ones.
4. Definately. Try a wrecker or toyota spare parts. Not sure if there is aftermarket ones. Don't forget the Unleaded fuel only sticker.
5. No.