I got the Catalina upgrade notice this morning but didn't click on the button because I don't feel I know enough about what sound like substantial changes. Please update with your experience as you sort things out. Thanks
In my experience the Apple Music service absolutely will destroy your music library. I joined and it immediately substituted it’s own lower resolution files for every one of the AIFF files I’d ripped from hundreds of my own CDs over many years, along with any other files that were the same song as ones in the Apple Music service. It took months to restore my library after turning off Apple Music but it wasn’t possible to restore everything from the originals I no longer had access to. iTunes has always worked for me but I'm waiting for more information about the Music functionality in Catalina.