Ok, I'm back.
For personal reasons, and because of Pictus' suggestion that I might wait until the New Year for some parts, I have not yet built this machine.
However, I would now like to proceed with the project asap.Here
is my current parts list.
Just to reiterate, it will be used for video editing, and the editing of (on occasion) very large still-image files.
Also, when batch processing large still-image files, I want it to move quickly.
Basically, I want a "Porsche-with-a-keyboard".
Any final advice appreciated.