Max,
You're tank isn't remotely large enough for a unicorn tang. You'd need an 8ft long 240gal tank (at least the very least) to keep that fish. Someone did tell you they grow to 24"
, right?
Its okay for now, but surgeonfish do grow fast. I'd say you have about 2 years tops before you'll need to find a new home for him.
That being said, you're already kind of full up on fish. Everyone seems to be overstocking these days
If you get rid of the unicorn tang, you'd not only free up a lot of room, but even more bioload (tangs are high bioload fish per unit length). I'd say go with the anthias. For me, green chromis were a bit fo a disapointment in terms of socialization.
Matt