How do I get the latest songs with the latest metadata info and combine my libraries together?

If this question has been asked then, I apologize. 

First I have a mess on my computer. I have lots of cds which were digitized into iTunes. Songs and music I do not want to lose. I do not have Apple Music and do NOT want to get it. Although I had it for one day and it messed up my library and I lost it. I immediately cancelled Apple Music. Eventually found the music library and made a copy of the songs. Used only iTunes and made several copies of the songs. Went through an macOS upgrade and iTunes was no longer, only Music. Used iTunes and imported the file into Music. Became a pain.  Now I use Music all the time.

Now I have 5 copies of my music libraries in one form or another on an external drive.

My mac is old, iMac late 2015, 27in, 3.2 intel core i5, 24 gb memory, macOS Monterey 12.7.6.

The "comments" section in iTunes is very important to me. This is where I keep the important information, EX. 'group, woman, vocals, noddin' . This is from latest comments. From earlier comments: EX. 'noddin'

I also have several copies of the 'x.itl' file. 

QUESTION: How do I get the latest song with the latest metadata info and combine my libraries together with the least amount of work? I want 2 of same libraries with same info because eventually I would like to get  iTunes Match. One library I would like to keep for me and the other for Match.

Can you suggest a book where I can understand iTunes, Music better?

[Re-Titled by Moderator]