My wife got me this for Christmas:
Star Wars: The Jedi Path and Book of Sith Deluxe Box Set
https://www.amazon.com/Star-Wars%C2%AE-Jedi-Path-Deluxe/dp/1452126410/ref=sr_1_3?keywords=book+of+the+jedi&qid=1577986717&sr=8-3It's not something I would typically get, but I read through it and it was kind of cool. Looking on Amazon, it shows this was released in 2014. However, I swore I saw a 2019 date when looking in the actual book. I need to do some research on whether this was updated, because there was a lot of stuff in here which seems to have been written to explain what we saw in TROS.
A few off the top of my head:
From the Sith Book:I had trouble getting through this because a lot of it just didn't interest me. But there was a lot of history on the Sith and apparently they were a race of people. And the fallen Jedi went to their planet and took it over to become their rulers. A caste system was setup where they act as engineers, workers, etc for the Sith. It's likely these are the Sith Loyalists we see in TROS. It specifically mentions the engineers know how to design a 'star killer'.
It mentioned the power Palpatine showed at the end of TROS where he sent the lightning into the air against the ships.
From the Jedi Book:It discussed how a Jedi can project a doppelganger like Luke did in TLJ.
It mentioned that Jedi using lightning (as Palpatine does) is something the Jedi are able to do, but is forbidden.
I dont think this means anything, but it specifically mentions that the yellow saber color is for the Jedi Sentinels. When you become a Jedi, you can go into one of three branches. This is one branch. But it sounds like those who fail their jedi trials can also go into this branch. My thought is that Reys saber color in TROS doesn't really have anything to do with this.