The instructions have been updated to reflect the doublers...I just checked. There is nothing in the SB that you HAVE to know since you'll be installing the doublers as you build (the SB is mainly for folks that need to retrofit), but reading it would fall into the "best practices" category. There no such thing as learning too much when it comes this this journey.
The one piece of valuable information that I did take away from the SB was on near the end (pg 17 maybe?) regarding edge distance. For the outboard most holes on the top of each doubler that get match drilled to the through the 702 spar and into the HS-710, edge distance of no less than 1.25D is acceptable (a deviation from the standard 2D). D in this case is the diameter of the rivet that will be set in the hole and the edge distance is measured from the CENTER of the hole, not from the edge of the hole.
Example: 1/8" rivet applying the 2D guideline requires that the edge of any material in which that hole is drilled is no closer then 1/4" to the center of the rivet hole.
Another tip worth considering is to build the vertical stab first. I actually paused my HS build and worked on the vertical for a period of time and found it much easier to assemble. The HS has a lot going in the center section and great care must be taken to get it all correct. Building the VS was a good confidence builder that made working the HS a more comfortable experience.