Obviously I'm answering this as someone who wasn't born till well past the Classic Motown days [[1975), but I figure I'll try this survey myself.

First time you heard the Supremes on the radio? During my childhood, listening to the oldies station from Detroit [[104.3 WOMC).
First time you saw them on television? Never on TV, took till the invention of Youtube to see any of their TV performances.
First single you owned? "You Keep Me Hangin' On"
First album you owned? 1974 Anthology on cassette.
First time you saw them in person? Never have, sadly.