Thank you for the detailed question, but from what I've read I'm confused - are you using external storage or not? If you are, how and what storage paths are mapped?
Also, regarding media files, I think this is a separate question, but when you exported and imported media files, did you check "Export physical files" checkbox in export wizard and likewise "Import physical files" in import wizard? Note, these are not checked by default if you were using just default settings. That's why you probably are getting empty images.