I think you get the Gold Mario driver
Nah you get Gold Mario for getting at least first in every 200cc cup, no need to triple star 'em. So I already have him.
Gold Kart is unlocked by getting at least one star in every 150cc mirror cup*, Gold Tires are for beating all the staff ghosts, and Gold Glider is at 5000 coins total.
Working my way through staff ghosts now, and I should hit 5000 coins through normal progress at time point.
*Was wrong about how to get the Gold Kart, but either way I got it already lol.