Having hard alkaline water sucks, doesn't it?
All the amazing fish like cichlids (I'm in love with rams, apistos and discus!) and other tetras all only flourish and breed in soft acidic water. Most of the fish that I don't want are fish that live in hard alkaline water (huge south african cichlids).
I'd say neons are a great fish. I was skeptical at first, but they look fantastic in my tank, and they don't really hide a lot. Although they stay near the bottom, they stay at the front of the tank. However cherry barbs are active fish so neons would probably be quite timid around your current stock, as you seem to have active fish.
I'm not sure how different the celestial danio is to the common zebra, but my guess is it'd be very active and a fast swimmer.
I've had platys before, and although they are very cute they don't really do anything... at all. And they poop, a lot. Like most livebearers.