... does anyone know if this machine has diagnostic LEDs like the older iMacs?
There are no diagnostic LEDs on the logic board.
I'm thinking it's definitely a hardware issue at this point but I don't know how to move forward, I figure I can at least recover the SSD.
This is a big jump in determination when two very conspicuous clues were presented:
The error has to be in the names of the directory structures you use. For example, using the last command the error must be in the names
There is a problem with one of these names or else there are no jpgs in that directory.
The same applies for the other ...