In this post I'll focus on what the section tells us about the translation.
This section refers to the "plates of Nephi" five times.
Key point 1: These passages make no sense if Joseph wasn't using the plates to translate. If he was merely reading words that appeared on the stone in the hat (SITH), he wouldn't know or care what was in the stack of plates he obtained from Moroni's stone box in the hill Cumorah.
38 And now, verily I say unto you, that an account of those things that you have written, which have gone out of your hands, is engraven upon the plates of Nephi;
39 Yea, and you remember it was said in those writings that a more particular account was given of these things upon the plates of Nephi.
40 And now, because the account which is engraven upon the plates of Nephi is more particular concerning the things which, in my wisdom, I would bring to the knowledge of the people in this account—
41 Therefore, you shall translate the engravings which are on the plates of Nephi, down even till you come to the reign of king Benjamin, or until you come to that which you have translated, which you have retained;
45 Behold, there are many things engraven upon the plates of Nephi which do throw greater views upon my gospel; therefore, it is wisdom in me that you should translate this first part of the engravings of Nephi, and send forth in this work.
(Doctrine and Covenants 10:41-5)