Besides Eminem, the other origin for "stan" that I've heard is that it's a portmanteau for "stalker/fan." I've seen it as a noun, but "stanning" is also a verb. And I guess "stannish" might be an adjective? Anyway, I've mostly heard it in terms of one's favorites - favorite character mostly (I'm such a Klaus stan!) rather than something more general (I'm a gadget stan!)