1) I believe after the song has progress past 50%, it will count as played. There is also Skip Count.
2) MC will write out file tags, and the other MC should pick them up. There is also
Library Server.
3) Files can be
Stacked, and this icon indicates the file's status in the stack.
4) You could use Playlists or your own user field to indicate that a track belongs to virtual albums. However, Album has some special properties, as MC internally does some work on tracks that belong to a single Album (volume adjustment, album art, setting the status of album completeness, etc.).
5) If the CD lookup data is bad, you can correct it using tools such as Find & Replace, etc. Then, resubmit the data to JRiver so the lookup is better for the next person down the line.