No offense, but you may want to do some more research before you get anything. Asking about harlequin shrimp with a starfish raises a pretty big red flag, since the only thing those shrimp eat is starfish.
Also, any kind of cucumber can be deadly. When they die, they'll release toxins in the water that will likely kill everything in your tank. In my opinion, they have no place in a reef tank, unless you fully understand their care and the risks, and have a great deal of experience.