As butterflies go, the pyramid is pretty reef safe. Fits the visual niche of a tang without the attitude. I think a 90 gallon is doable, but kind of marginal for a pyramid. I'm apparently alone in this, but I wouldn't put any of the large angels in a 90, including scribbled or regal angels. I had a majestic in a 90 for a while, but I ended up feeling bad about it because he was kind of stunted. I don't think I'd do that again.
As people have said, there are a lot of dwarf angels that would work in a tank that size. It's not a dwarf, but the singapore angel doesn't get terribly big and it kind of looks like a butterfly so it might work for you. You may have to look around to find one that eats, that is (which is kind of tricky). Same for multibar angels. Gorgeous, and once they're acclimated and eating, they're pretty hardy.
Chromis are likely to whittle themselves down to a single individual or, if you're very lucky, a pair. They're also prone to uronemia. If you want a group, cardinals (but not banggais) may be a better option. Maybe yellow stripes?