I am adding a workshop, and upgrading my service from 200A to 400A. The Shop will get a 200A panel and the existing House panel will be backfed from the main. I want to bring the new House feeder into the existing meter base and install my own private GE electric meter. Can I use any serviceable 200A single phase 240V meter such as I might find refurbished on EBAY? like the dial ones, versus the digital ones? Does NEC have any rules on installing my own meter?
Yes, you can do that and as you have noted, there are many used KWH meters for sale on EBAY and other places. A properly installed meter base along with a listed meter will do what you want and be compliant. It's not uncommon for such meters to be used with solar energy systems and such.
I recommend the old-fashioned mechanical kind vs. the new digital models. They are simpler and more reliable in my opinion plus they look cool. I like the spinning disk vs. a tiny LCD "spinning" one way or the other.