re: Advice on calculating portions in a carved cake please?

I agree with Donna, put the car on a sheetcake road then make the car the size you’re comfortable with. If you have to make the car serve 80 you’ll be a total wreck thinking about it. If she is truly your friend, she will understand Non-cake people have no idea how time-consuming planning something like this out is and most of us don’t get paid properly for our pre-baking planning sessions.