With all the fles on the external drive, as Pete said you may struggle with playback. However you can opt to used proxie media for this. It's a lower quality version of the original but is smaller in file size and speeds up playback. Rendering however is done from the optimised media, so no quality loss.I would also suggest , if not done so already, upgrade to the latest version of FCPX. As this version saves Motion templates ( i.e custom tittles etc.) within the project library, which earlier versions did not. This means that everything is within the library so it can be opened on different computers. However the 10.3 interface is different fom the older version so takes a bit of getting used to. There are several video's on the web explaining the upgrade