Noa is lovely.
Noah is a boy's name though, so I would think it odd if I met a girl named that (just as I would with a girl named after say, Jacob, Esau, Ezekiel, Micah, Issac, Benjamin, Joseph etc).
Sydney (and Sidney come to that) has been used for girls for a couple of centuries! I don't think there is any consistent reason for how names become unisex (Kimberley, Ashley) or change completely (Tracey, Marion, Shirley), but the only "measure" is general acceptance. I don't think the major male OT names are anywhere close to that - especially as that Book features in three major world religions.