I’ve edited an entire feature film in FCPX as well as a number of dramatic shorts. Everything can definitely be in a single library. You can have the entire film in one timeline (project), but it gets unwieldy for active editing and adjustments. This is especially true if you start adding something like an adjustment layer with a LUT or a timecode or a title over the whole timeline.
My strategy is to cut each scene as its own project. Then combine scenes into reels and then reels into a final timeline. I keep my working versions along the way. So I will have tons of projects (sequences) of varying lengths by the time I get done. Depending on how you mix, color grade and/or distribute, you might have to deliver in reels anyway.
I would also recommend working in proxy media, using FCPX’s internal proxy function. Typically I’ll keep the original camera media external to the library, but generated proxies can be inside the library, if you like.
– Oliver
Oliver Peters Post Production Services, LLC
Orlando, FL
http://www.oliverpeters.com