So it appears you can conveniently query the DB for filename (+directory), UUID, and (original) file size. But I can't find a good way of opening a Photo by filename or UUID.

After all, the file might not be present locally, so opening it should go through the Photos.app. But once you call AppleScript to open the file, you might as well use the AppleScript to comb through the database like the script I linked to earlier.