If its a 70something bowfront, I would not have the yellow tang and would trade for a Kole, Tomini or a tang that will work long term in there. Consider a mimic Lemonpeel instead?.
No way on the Hippo. Needs a tank at least twice that. Its begging for health issues otherwise.
Copper bands are very difficult fish. Picky eaters, need very established tanks to graze in and do not do well with anything remotely aggressive (which the tangs and angel would be). They also need a much larger tank. Butterflies in general are tough to keep, but copperbands are notoriously difficult.
If its 721 gallons, get the Hippo.