If you export your records and import the files again the new records will have new UUIDs, i.e. existing item links won‘t work anymore. That’s of course only a problem if you‘ve used item links in the past.
If you need to keep the item links use this approach:
Step 4 is not necessary anymore due to tighter integration with the Finder.
No.
You could of course index each subfolder separately, but in this case you’ll have to index new subfolders manually.