With regard to restrictions in Aus, particularly Tasmania, I found this website to give a good overview of the different restrictions by hire car company:
https://www.drivenow.com.au/vehicle-usage.jspc
(As always, check the T&Cs before you buy with whichever company)
As has been said, some hire car companies expressly prohibit something whereas others will have restrictions that basically mean you are not insured for losses. Examples include taking the car inter-state, on certain ferries, on Bruny Island, on gravel roads, on roads above the snow line and in case of hitting wildlife.
There was some interesting research recently about how often tourists drive at night:
Tasmania tourist tracking
Dr Hardy said many tourists travelled long distances by car, often late at night.
"We found that they were leaving Hobart quite late in the day for some people, going up to these places which were a four-hour drive away and then returning at night time," she said.
"So in terms of protecting wildlife, ensuring safety, those sorts of things were really significant."
For the OP, also be aware some of the more minor roads in northern Tasmania are still being repaired following the major floods in June 2016, but there are generally ways around. Enjoy the planning and enjoy Tasmania!