Looking through enamdict, there's around 30 or so entries for Minako. I suspect most of them aren't used regularly, however.
"ko" is easy, it's just "little one". A lot of Japanese girls names use "ko".
"Mina" means everyone. There's a way to write Minako so it has the "everyone" kanji in it.
"Mi" in a girl's name usually means "beauty". Many transliterations of "na" exist, but has a "what connotation" in one kanji-zation, and "vegetable" in another kanji-zation.
I have thoroughly confused you guys, haven't I? (It makes a lot of sense to me since I am Chinese and therefore know some kanji, but the way I explain it is really weird.)
Anyway, as a side note, "mina" is everyone. However, most English fan anime websites you see use "minna", which is incorrect.