What symptoms will they have?: Gem will take the flu symptons but with a canon twist. He's got an illness in canon that requires him to ingest demon blood on a regular basis. When he cannot give it to himself, his fevers will spike and he will cough blood.
What will their essence rite will be?: Jem owns a jade necklace that was his mothers. Finding a piece of jade and restore him.
What is the dream hinting (or outright telling) helpers about the essence rite like?: He will appear in a dream and also ask for the demon blood. He will tell whoever it is, if he goes to long without it, he will die.
Are you open to anyone performing the essence rite?: Yes of course!