The first verse is Nephi’s ending of the story of the dream. We get his segment-ending phrase “dwelt in a tent.” As with other times when Nephi speaks of his father’s tent, or his father dwelling in a tent, the function is to separate sections of the story being told in the larger chapter. What is most important in this case is that Nephi makes mention that many other things happened “which cannot be written upon these plates.”
That phrase obviously mentions plates, and apparently it finally occurs to Nephi that he hasn’t explained to his readers the various plate records he is working with. This creates an aside. Nephi moves out of his role as the narrator of history and into his role as the writer of history. He speaks of his process. He will do this a total of three times. The first (being this one) and the second are both insertions by Nephi the writer into the narrative story. Finally, the third time will be a short explanation of creating the plates in the narrative timeline that actually produced them.
Nephi notes that there are two sets of plates. He has made both sets by hand (though that is not mentioned here), and he is (at that time) the only writer on both sets of plates. He also explains that each is called “the plates of Nephi.” The designation of the small plates of Nephi to refer to this current set comes from Jacob 1:1, where Jacob describes them as “the small plates, upon which these things are engraven.” The term “large plates of Nephi” is derived as a counter to the small plates.
Since Nephi made both sets, it is probable that he made them all the same size. Since the plates of brass were so important to him, it is also possible that their size, and perhaps even color, influenced the size and materials for the plates Nephi made.