Photos Storage and Transfer Safety

Greetings!  Had a question with regards to maintaining all the excellent features in the photos app.  

How should I export all the photos in the library, to an external SSD/HHD to maintain the full quality, original photos?

Option 1: Find where the photos are saved in finder and click and drag

Option 2: Select all photos in the library and click "Export."  From here you can click export.  

Option 3: Same as option 2 but rather than click “Export," click “export unmodified original.”  

When doing it by way of option 3, you are presented with the option to “Export IPTC as XMP,” which is in an “export original” option box.  I have already clicked “Export Unmodified Original” Why is this an option?  Having this extra, seemingly redundant option, makes me wonder if there are other hidden options in the other methods, to set up the correct transfer.

Concerns and ReCap 

Will the click and drag method include all the original metadata that I would have to manually figure out the latter options? Will it include the same features as “Export IPTC as XMP”?

I need to be sure that I am saving a good file source, I am upgrading my mac and don’t want lose any of the precious details.  I’m only interested in local saved copies, not iCloud.  

Thanks in advance! 

Steve