What symptoms will they have?: Carla will be having presence sickness. She will also be flipping her shit about it because being forgotten is her worst fear in the world.
What will their essence rite will be?: Blood and misery. Killing or torturing/harming others, either physically or psychologically. Cannibalism optional.
What is the dream hinting (or outright telling) helpers about the essence rite like?: ...Blood and misery. Killing or torturing others, either physically or psychologically. And eating them. Very violent dreams, sexual bent optional.
Are you open to anyone performing the essence rite?: Yeah, but it's the kind of rite I don't think most will volunteer for.