Media. I have copied all my media folders, in the structure I had them on Legacy, into FH7's media folder, and deleted all the media which was ih FH7 base media folder. Result I now have about 4000 unlinked images, documents, etc.
To re-link them individually would take more time than I've probably got (I'm nearly 90).
So, if you can make any suggestions I will be grateful. Is there a plugin or is FH able to do it?

FH should be able to repair the links for you.   Use Tools > External File Links.  Then click the Auto Repair Links button.

That doesn't do it. It finds them, renames them and puts them back in the root media folder, in the process deleting all the named folders I've made.
My system is, i.e. for Census, folder named census, sub-folders named "Counties, media files names "Year of census Name of Head - Database I.d. number.

It shouldn't be renaming any files at all, it simply adjusts the file paths where FH is looking for the files.  And it can't delete the sub-folders you made. 

This is from the FH Help files, explaining what the Auto Repair Links button does:

This button will prompt Family Historian to attempt to find missing media files and fix any 'broken' links. This can be a slow process, but a progress dialog is displayed so you can stop the search at any time if you wish. The search will begin with the current project folder, and ripple outwards from the current project, eventually including other fixed drives on your PC if necessary (and if there are any). The search will stop automatically when all missing files are found. As well as finding missing files, this function will also check if links to media files in the media subfolder of the project folder are setup as they should be, and will automatically fix the links if necessary.

That doesn't do it. It finds them, renames them and puts them back in the root media folder, in the process deleting all the named folders I've made.
My system is, i.e. for Census, folder named census, sub-folders named "Counties, media files names "Year of census Name of Head - Database I.d. number.

_._

It renames them Q###. I've deleted them so can't show you. I still have them in my Legacy folder - which I'm not going to remove - instead of finding them in it's own media folder, it seems to prefer looking everywhere but there!

Derek, the Auto Repair Links operation in FH cannot rename any files on your computer and it cannot delete any sub-folders.  It only adjusts file path links.  I can't explain what went wrong but it was not caused by FH.  Please try the process again, keeping several screenshots:

1. A screenshot of the Media folder showing its sub-folders (after you have created the sub folders and their contents again but before you run Auto Repair Links)

2.  A screenshot of the Tools > External File Links window before you run Auto Repair Links

3. and 4. Screenshots of both of the above after running auto repair links.

I have finally sorted it by a combination of zipping all the folders I didn't want including, then deleting the original folders, and amending the gedcom so that the wrong links were  corrected to the correct ones. Before you raise you  r hands in horror at me interfering with the gedcom, maybe I should say that I have nearly 50 years of computing experience. But thanks to all of you.
Now i have to try and find out why Text from source shows so few choices!

Family Historian can, and does make copies of files with new names as Derek stated.  It copied and renamed 616 copies of my photos.  A snippet of a partial listing of the 616 is included as proof.

In addition, I found them in multiple folders.  That is likely due to me attempting to move my photos to a specific folder.
--
Mark Trevithick

The first photo in the screen shot is named "001 Mark in Payson - 2019".  Before being copied and renamed, it was simply "Mark in Payson - 2019".  The 001 was appended to the name all the way up to 616 for the 616 files that were copied.  The folder structure on my computer for genealogy photos is "E:\My Pictures\Family - Genealogy\Photos".

Initially, I started a new project with a 5.5.1 gedcom file exported from Legacy.  I do not recall if it copied/renamed them at the time, but it did not create links to their true location.

After becoming frustrated, I created the file structure as used in the Sample Family "E:\Documents\Family Historian Projects\Family Historian Sample Project\Family Historian Sample Project.fh_data", and after numerous attempts at limiting where they were located with no success, I cannot accurately tell you what I did.  One person on the Forum suggested not leaving the default box checked on import.

I ended up with a mess, and am attempting to sort through all the different advice on how to setup correctly.

Thank you for your response.

Mike Tate has also responded with a link to a document that I will read.

Blessings,

Mark Trevithick