@matigo Fortunately it was mostly a matter of importing many Lightroom catalogs into a new master file, relinking the folders (links broken due to having changed external hard drive setups over the years), and upgrading the old catalogs where needed.
The harder bits will be normalising all the keywords I've used over the years, and the way I've marked the "picks" of shoots: in recent years I've had one folder per week/month of general snapshots, and then a dedicated folder for each event in which "picks" get rated 5 stars, but I used to dump them all into the same folder and just put the picks into a manual Lightroom collection.