I don't think that you could use storylines, but while I've never tried it, I don't see why you wouldn't be able to use compund clips.
However since FCPX isn't the most stable application right now, if it does work, I don't know how stable this course of editing would be.
Yes, you can use video clips, audio clip, still graphics, and Compound Clips. Either in the Browser or in a Timeline. There's lot of cool and useful tricks you can do with auditions that most folks aren't yet aware of. My "Media Management" for FCP X course covers all of this at macProVideo. Very easy to do. But be aware Auditioning compounds that are very full may get a tad sluggish if they're really big. Simply a lot of data to process. That's why once you've made a decision on which clip to use it is recommended you "Finalize" your Audition.