Backup Organizer in OneDrive questions

All my images have been saved in OneDrive. I just started to work in Elements 14 and imported all 18,000 images from OneDrive into Organizer (perhaps a mistake?). I am following a Lynda tutorial and just learned about the backup function. My questions are as follows:

If I backup my Organizer to OneDrive, am I creating a second set of 18,000 images (albeit with the metadata)? Should I instead backup Organizer to my external hard drive? Is there a way to backup only the metadata so I won't duplicate the backup of my images?

Thank you for providing any advice.