While the number of files is important for the scale of the operation, keep in mind that what makes it illegal is deliberately withholding the documents and lying about returning them all that he is being charged with. The crime is trying to keep them when asked to return them and deceiving federal agencies, not just taking the files themselves
It's one thing to have a couple files misplaced within your stuff when leaving the White House but this is ridiculous. He definitely had all this to sell to other countries.
I'm willing to bet there is a lot more at other locations. This looks like a general dump. Anyone with this kind of hord is going to keep their best stuff in special places.