Not legal in QLD either, all i can say is if you do use them , make sure you use some high quality wheel spacers from a known brand, made of a billet aluminum, these will be at the very least as strong as the wheels that you are attaching them too, if you go ahead you will increase the offset of the wheel, by doing this you also place more stress on the axle’s studs (but not much more than a larger offset would give you) you may need to fit longer studs to compensate for the width of spacer you use, cheapest way out if you are only using max 10mm would be to purchase extra turn wheel nuts to give you necessary torque to attach mags safely, this still wont alleviate the increased stress on the studs/assembly, but at the very least your wheels wont fall off!
I would recommend only using a floating spacer (cheapest) but only up to 10mm, most common size is 3mm to 5mm, otherwise you would go to another 1 of the 4 different types available.
By increase the offset more on these already wide rims you will increase the chances of your tires scrubbing on your outer inner guard area, this can be compensated only to a certain degree by suspension modifications/ and or inner guard/lip modifications, and as you stated you have a stock coupe? Oh and just another small point, if you happen to have an accident for whatever reason insurance will wipe you and deem you responsible if they see wheel spacers, let alone the wheels.
I don't know if you have the wheels or not yet, i guess not, otherwise you would not be asking, so maybe you could check out if any mates/mates friends that have a similar offset 18/8/ 40 series multistud on their car you could test fit to yours to check everything out.