You can just move and/or copy whole Events and Projects within FCPX directly.
Just make sure that the "Event Library" on the left is shown (if not, you can press Cmd+Shift+1). There you will see all hard drives (internal and external) that are currently connected to your computer. And, in a Finder-like manner, the Events and Projects are listed on the hard drives. Just drag and drop the Project to another hard drive to copy it, or hold down Cmd to move it. You will be asked if the Event containing all the data should be moved along with the project.
It's as simple as that. 🙂 Hope that helps.