Its been a long time as I ran CoCT several years ago. I am not famaliar with the recent update.
From the other posters it seems the encounters have been upped, I would trim them down judiciously.
Scarwall worked well for my group as the focus was on accomplishing the mission re the soul anchors it helped drive the dungeon crawling and give it some set objective as opposed to walk down halls, kill stuff. The rping in this dungeon setting was quite memorable but that can only happen by the GM providing good opportunities for the party to understand the background and situation. IIRC, I used the hag to provide a lot of facts (after the party subdued her). It wasn't really planned but seemed like a good opportunity to convey info that Laori and Sial wouldn't necessarily be privy to (or wish to share)
Re how to fight undead at this level the PCs should have reasonable Knowledge skills and advice from Laori, Sial. Info dumping should be straightforward. The importance of Deathward spells cannot be overstated.
Re maps, don't try to map out the whole castle, just do the rooms you need either done ahead of time (1 inch grid paper can be found from stationary store pretty easily) or just draw them as needed. Maybe have a flip mat or two stand in for important encounters.
Re Laori/Sial I can't quite remember what happened but the party had a falling out with Sial so Laori was the only NPC to worry about. Sial is pretty disposable.