As cars get smaller engines these days, we might have to include 6 cylinder (even the old Jag XK220 was a V6).
But usually they are 8 or more. Some have electric boost but that's not exclusive to supercars.
Dare I say some might be fully electric?
Generally 2 seater. Didn't the McLaren F1 have 3?
Generally designed to be driven on a track (if required) a bit like Range Rover are designed to be driven off road except most aren't.
I'm not sure mid engine is critical. Plenty of rear and front engine supercar, though some might be considered GT cars.
Expensive and exclusive
Essential: must be Italian.
Good luck with the R8. Must say I do like them.