[dnanian]

User files are considered to be in the /Users folder -- it's completely location based. Your music, photos, etc remain on the original drive and are shared (symlinked) to the Sandbox.

You would, indeed, boot from the Sandbox/Safety Clone on the external.

As above, the /Users folder is really on the original drive, and the contents aren't copied, only shared/linked.

Hope that helps to explain...