One thing to help prevent confusion...
*iTunes library* is the *iTunes library file* in the Tunes folder and also it is everything you see when you open iTunes. It is not the *iTunes music folder* or the *iTunes folder*.
I noticed that the place where my itunes library is -
The *iTunes folder* or the
iTunes music folder?
Do this...
Click the icon to launch iTunes then immediately press and hold the *Option * key.
Select *Create new library*. Select the external hard drive with all the music.
This will create a new *iTunes folder* on that drive.
Move all your music directly into the _iTunes music folder_ in this new folder. Don't worry about correct folder names or anything. iTunes will take care of it.
Once you have it all in there, File -> Add to library and select the iTunes music folder on the external.
No need to change the iTunes music folder location in iTunes prefs. It should already be pointing to this new folder.
ONce you are sure you have everything in iTunes you want, you can delete the music wherever else it is.