Are you in a good biome? Otherwise undeads shouldnt just die.
Vcordie: Warlocks have fancy names, each different name is for a caste, each caste has a different spell. Nothing special about them, really.
Strand-Extraction is a vanilla limitation. And I still dont think that priests are so bad at embark. 2x (with harder learning 4x) faster praying skill is quite a hefty improvement, and the little, free altar can give you quite an advantage.
blackdot, fertilizing once should be enough.
To whoever asked
"Is a religious/altar based fortress possible?" the answer is Yes. You can power a fort just with prayers. At least for the raw materials, of course.
You still need normal labors to refine those into goods.