Moving my iTunes data

Coach,

Just to be clear, are you importing those files so as to make one single library? if so, do them in smaller batches.

iTunes/Music is famous for choking when you do too many files at once. You may need a little trial and error to figure out what size batch is acceptable. Once you verify that the batch has processed into the library, do another batch.

Coach,

Those instructions tell you where it will place any new additions to the library. (Notice the "from now on..." bit.) It doesn't move anything unless you continue to the "Consolidate" step.

If you want to continue to have multiple libraries, you can do an Option-Start each time, and tell it which library you wish to use for this session. Details can be found here: Use multiple libraries in Music on Mac – Apple Support (UK)

Or, if you want to create one big library, pick the one you want to start with. Then find any files that are not already in that library, and add them in. See details here: Import music from a computer to Music on Mac

Import music from a computer to Music on Mac - Apple Support

For any of the above, pls make sure you have a decent backup before moving things around. It is unfortunately very easy to mess things up!

Coach,

Not sure which Apple help instructions you followed, but it sounds like you moved that library to a new location, which is different from adding its contents to another library.

Also, when you reboot the computer, you may be changing the drive letter of the external, which will cause iTunes to lose it.