50n0f508: Ok...so in order to move the iTunes library to my local OneDrive I will have to make a copy to my external drive, delete it on my PC to free up disk space, then use the external drive to copy the library to my local OneDrive folder, which once complete will sync to my online OneDrive?

That would work, but it's more complicated than I was trying to suggest. 

I was just thinking you could move the existing iTunes folder (by drag and drop within Explorer) from it's current location (which is presumably under your "Music" folder in your profile) to the cloud-sync folder (which in my example above would be "Box Sync" in the user-profile).  Then re-run iTunes with the shift-key held down (from memory), and then navigate to the relocated iTunes folder.

The "Drag-and-drop" in Explorer would be a "move" rather than a "copy", so it would be much faster, and wouldn't take up any more additional space on your local hard drive.

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Having said that, your method would work, although it would take a little longer to copy to/from the portable device, and it does have the advantage of having made a backup copy just in case something goes horribly wrong with the cloud-sync process...

As with all things in computing, there are multiple solutions/approaches to how to do this.