I'm with J2T on this one. I had one in a 3 gallon pico and he was fun, but I don't think you'd ever see it in a 75g. That said they're not horribly expensive, and it's always fun when someone shows up that you've not seen in a while.
As for the copperband I'm unsure. The crabs are pretty timid and I think it is quite possible that they'd be pretty easy to make a snack out of.