Hi, bassdon,
iMovie 10 projects cannot be stored independently of the iMovie library in which they reside. So you cannot transfer them independently to a Finder folder as you would like. To store a project on an eternal drive you must either transfer the library that contains it to the external drive, or create a new library on the external drive and transfer the project to the new library. The external drive must be formatted Mac OS Extended (Journaled) or APFS. Mac OS Extended (Jornaled) would be compatible with operating systems previous to Sierra.
If you transfer the library you should first select the library name in the sidebar and do a File/Consolidate Library Media to make sure that all of the media in the library is transferred as well. If you transfer only the project to a new library on the external drive, then you should select the project icon in the project browser view and do a File/Consolidate Project Media before transferring the project -- again to insure that all of the media in the project stays with the project. You must keep everything together to insure that you do not have missing clips in the project.
I'm not sure what you mean by "information pertinent to each individual song". A background song in an iMovie project will show the title and duration of the clip in the timeline or in the browser view if you have View/Skimmer Info checked from the menu bar. To get anything more than title and duration you would need to select the clip and do a File/Reveal in Finder, and then do a Control-click/Get Info of the file from the pop-up Original Media folder.
-- Rich