1. 1:1 people who "belonged to King Benjamin" is a very feudal, pre-modern formulation. Sounds like a reference to the multiple ethnicities that make up the kingdom of Zarahemla.
2. 1:2-4 confirms that this is a different line of Lehi's family. I guess Nephi gave his small plates to Jacob, and the "man" anointed by Nephi to be Nephi II in Jacob 1:9 was some other family member.
3. 1:3 tantalizes with its reference to the "mysteries". Literally, it seems to say that the brass plates enabled Lehi to preserve temple ritual among his people. As a prolog to Benjamin's great temple address-farewell sermon, this makes great sense. This puts a different nuance on Nephi's internal debate over killing Laban in 1 Nephi 4:12-18.
4. 1:5 hits the "mystery" bell again, and seems to say that's specifically the thing the Lamanites have lost.
5. Typo! My copy has an asterisk in 1:10, with no footnote. That's what I get for reading closely. Ha!
6. 1:10ff sounds like court ceremony. I think it's likely everyone was already gathered for the fall festivals, and this summons (Benjamin "had Mosiah brought before him") was a bit of theater that was part of the prelude to making Mosiah co-king with Benjamin (1:15ff).