File management- preventing the deletion of files referenced by nodes
This is for them primarily images and PDFs which they intend to add to the server via FTP.


No... I would advise installing the Media Entity and set of modules designed for handling media.

This will allow you to add media in a way that has better treatment than core. You will be able to:


Use one file in multiple places without uploading it again 
Build displays based around media, if you need to 
Add a button in CKEditor for referencing or uploading new media


If you only upload files in an FTP, you can't do basic things, like:


Resize an image with an image style
See how many times / where an image or file is being used
Generate different displays for different files
Create Views based around media which may be mixed with access grants later on (spitballing)


Core upload fields, or FTP copying, will not grant you anything - and giving non technical people access to FTP instead of a GUI backend like Drupal is far more error prone.

Also, there is a known core issue where files can be deleted without warning, and it is suggested to set the core file system setting of "Delete orphaned files after.." to "Never". No matter how you choose to approach media management, change this setting ASAP until it is fixed.

One of the major benefits of moving from a static setup to Drupal 8 are for reasons like this.