I'll chime in here, but not to add anything to the question of which books to read in what order, but more to clarify some things.
First off, the Manticore Ascendant "prequels" were not just written by Timothy Zahn (coming from the SW EU, I figured you'd know that name). They were also co-written by David Weber and Tom Pope. Tom is the driving force behind BuNine (
http://www.bunine.org ). While Tom isn't credited on the cover of the first Zahn collaboration as a co-author, I believe he is credited inside, and last I heard, he will be credited on the covers of the two follow-up books.
Next, BuNine is an organization of fans who work directly with David to flesh out the history, politics, governmental and military organization of various star nations in the Honorverse. We also do the artwork that appears in
House of Steel: The Honorverse Companion, as well as writing the companion portion of it, whereas David wrote the novella,
I Will Build My House of Steel, which also appears in HoS.
House of Steel concerns itself with the SKM/RMN and the Protectorate of Grayson/GSN.
The next companion,
House of Lies, will detail background and history of Haven/PRN/RHN and the Andermani Empire.
There is a third companion planned as well, but I always forget who we will deal with there.
Anything written in the companions, or talked about by any member of BuNine can be considered hard canon, as if it came from David himself (known as runsforcelery - or RFC - here on the forum).
Lastly, if you want to see what is currently canon for what some of the ships look like, just follow the links in my sig. I'm one of the artists for BuNine, and you can see what my area is from the links. Keep in mind, these are still works-in-progress, and will most likely change, but only in the details. The general look is pretty much set in stone and won't change. We are currently working on adding more detail to the ships, concentrating on the HMS Fearless (CA-286), as that is our baseline ship on which all other ships will be built from. There's still a few things we need to work out over the next few weeks, but I would expect a major update to most of the ships on my Deviant Art page a couple of months from now at the soonest.