That helped but still some issues
I didn't realize that I can't import my personal comments/notes into the comments column in Calibre. I do see my comments in the book details panel and edit metadata view now, as you pointed out. Thank you kiwidude!
I have two follow-up questions - For some reason, the import list plug-in isn't loading my comments anymore, see new screen prints #2 & #3.
Also, I have books that I can't import at all (screen print #1), the 'next' button in step 1 won't activate. These books come from the same master csv list that I had broken down into smaller lists so that the plug-in will take them (doesn't seem to like big lists), and from which I've uploaded almost my entire book list. But even an excerpt of 5 books from the original csv list won't work now.
Would you know what is going on with these two issues?