I think it's very nice on paper. I can see the appeal to a name-nerd, as a name-nerd myself. But honestly, if I heard someone had named their baby
Amadeus, I would cringe. In my neck of the woods it would come across as painfully pretentious.
Definitely, definitely don't think it works on a girl. It ends in "us", it's not in a grey area. Amadea for a girl.