Generally speaking, you want your least-aggressive fish in first. So you'd go with the fairy, then the butterflyfish, then the tang. Honestly, I'd scrap the notion of putting in a copper-banded butterflyfish in that type of system, and only add the tang. Why? Because your clowns and pseudochromis are both rather aggressive. You might be able to stick the fairy in because it's a relatively fast swimmer, and I think that your clowns will stick near their anemone enough to keep the fairy safe and you can find a fairy that's dissimilar enough in appearance not to make the pseudochromis feel threatened. But I'd put it in before the tang. Definitely. And I'd scrap the butterflyfish because it requires a larger tank due to its activity level (I'm thinking of something along the lines of a 100 to 125-gallon instead of a 75).