Starting over with iTunes Match - but how?

I am in the process of rebuilding my music library and would like to move from Apple Music to iTunes Match. In that process, I assumed, that once I disabled Apple Music and activated iTunes Match, all there would be left in my library would be the music files actually present on my Mac.

But no. All matched/transferred songs were still there. Even music added as an Apple Music subscriber was listed, albeit unplayable. Even some of the matched songs won't play, and I find that very weird.

Now i wonder: Album A that is in the cloud but not in the actual library, will it appear twice if i add it to the library, or will it match up with the previously matched album?

Would it be better to unmatch/untransfer songs and then do the rebuild and do a new sync in smaller batches as albums are added to the library?

It's a large library.