Creating and using external metadata

For the last several years I have collected Spanish Textbooks with the idea of creating a library tool using Calibre as the reader device. It was more successful than I expected. Now with several thousand titles.

In the process I have created specific title selections at the request of a specific school with their requested books.

The practical problem is that it takes a long time to go through the individual files to code the metadata needed to present the books in a useful manner. As the requests grows it becomes more time consuming to update files with unique metadata for each school.

What is desired is to be able to create an external database (Spreadsheet) that would allow metadata to be easily updated for any or all of the new titles or schools in one place. That would mean I wouldn't have to open multiple file, rather just update the spread sheet which contained all the variations and metadata in one place, making it much easier to edit.

If a new file set could be made (based on the metadata) and then either directly imported, or copied into Calibre, that solve a host of issues,

Anyone else facing this issue? Any ideas? Any suggestions?
Thanks for your time and replies
Dr. Buz