Since Rayya has a head for all things housing, and is decent enough in a scrap, I assigned her to be the steward of Hjalmarch Hall - the Dawnstar property, and instructed her to buy a whole bunch of supplies and furnishings. While she did that, I returned to Riverwood to recruit B.T.'s sister in arms, Marauder, to loot my stash of ingots at Whiterun and the stash at Ravensburg castle.
With those we are able to construct the main hall which connects to the small house (now the foyer) and acts as the central hub to which other house "wings" can be attached. I start work on constructing the bedrooms but run out of quarried stone to finish the job. A courier finds me here, telling me that Ralis again wants my help at the dig so I instruct Rayya to put a whole bunch of construction items on the list of things to get too.
Two handy fast travels later and Marauder and I are at Ralis' site. This time -everyone- is dead, and based on his scattered journals, Ralis has been a servant of Azhidal this whole time, "feeding" people to him. Marauder easily clears out the risen draugr only needing my help in the final chamber where Ralis successfully awakens his dragon priest master, killing himself in the process.
Apart from all the draugr and the zombies Azhidal is raising, the dragon priest has an interesting shout that simply removes 25% of your total life. If only he used it more often. Upon his destruction, all the zombies and draugr "died" once more which happened to just save Marauder from being undead chow. After looting the place and collecting the black book at the end I am now at level 75, and it was time to head back and finish that house!
Yeah, house building sounds better than staying here with Shub-Niggurath.