One thing your going to quickly learn is the many LFS outright lie or don't really have any knowledge about SW systems. As for copperband butterfly they have a very long narrow mouth. It's made for poking about about a reef finding small things to eat. This can make them difficult to get them to start feeding. I'd not call it a difficult fish, but I'd not recommend it as something to start with.
I have posted this many times before, but I think you'll find it useful -
Standard Lecture #1 – Advice for people new to the hobby
The very first thing you want to do, before you spend any money on equipment or livestock, is get yourself a few good books on state of the art reef systems. Then read and study them, so you have some idea about what your are doing.
Here are two to start with -
The Conscientious Marine Aquarist by Robert Fenner
The New Marine Aquarium by Michael Paleta <---This book has an especially good section on fish suited to someone starting off in the hobby.
A note on the books. You can often find used copies at much lower prices at places like Amazon. In most cases these are going to be as good as new copies, especially when your first learning.
This is information that you can not easily obtain from the net. While it's out there, it's all over the place, and there is a massive volume of information. There is also a lot of bad information out there.
Once you get that done, plan or rethink your system. What do you want to keep? Do you have the necessary equipment? Do you have the knowledge to keep the livestock you want? Do you have the time to dedicate to keeping a system and it's livestock?
Many salt water fish, corals and inverts often have very specific requirements. Some are extremely difficult to keep alive, even if you do everything right. Before you get anything, research it, and be sure it will work out in your system.
Lastly, you will find that most LFS people are clueless when it comes to SW systems. Verify their advice, until they prove otherwise.