I sort of did both. First I imported everything I had into a Calibre library named Not Started.
Then I created a second library called Work Space, and used the 'move to library' function to put in books that I wanted to work on right now. Usually they are batches of one author or one series or whatever.
Then I fixed stuff up in Work Space. As I fixed it up, I moved it to another library called Completed.
So the Completed library is always nice and clean.
and the work space is the stuff I'm in the middle of, and the Not Started is one big mess.