I have now created an SQL file to create and populate the MySQL tables for the Drupal module. Whilst my original plan was to do an identical initial population with that I am using for DCMetaSpider, there were parts related to metadata discovery that would be irrelevant for the Drupal module - these have now been stripped out. Tomorrow, all being well, I will write a set of PHP functions (mostly wrappers around SQL) that will perform all the tasks required to insert, update and retrieve the metadata records.
It is beginning to look like this project will take less time than anticipated, but I do not know yet what delights await me in the Drupal API that might yet confound my efforts.