The Crow Key is used near the start of the game, not far from the bed. I think that's close enough without spoilers.
You can go to the Wolf Cult in the mines to refill everyone's hunger, if you're desperate. 50% chance of dying.
You can look for spell books in the libraries, sacrifice people, or use soul stones to learn spells, which tend to be far stronger than melee.
Outlander, you have to talk to him in the rabbit courtyard, then find him in the tree.
Dark priest, you have to talk to him twice and no more, in the library just before the rabbits, then in the library below near Legarde. You have to give him an eclipse talisman, which I think you get from the yellow mages.
Hope this helps!