So, good news! Made lots of progress. Broke the ice, raided the castle (and treasury), got past the death knights, and some minor quests done here and there.
I'm trying to find the blood of the mother, though, and I THINK it has to do with that church, but... I still don't know how to open the secret door. I found a skull cave, but it just seemed to have portals and a spellbook prize for getting through it. I haven't found anything else churchlike, but I don't know how to progress past the initial hallway in that church. Any hints?