Heck, this sounds awesome. The ghosts, as they are right now, are really quite underwhelming anyway.
If you play as one, they definitely should have different needs than when they were alive. They don't need to sleep, they don't need to eat, they don't need to pee, basically no bodily functions, because they don't really have a physical body anymore that would do those things! They're dead. Their body that would do these things is rotting underground or turned to ashes.
Perhaps if they died of starvation or something, they'd still attempt to make food, but they can't actually eat it and they'd make a mess because everything just phases right through them anyway.
Maybe there could also be a psychic medium trait that makes sims see ghosts from the beginning? Maybe as a reward trait, maybe a part of a new ghost-related aspiration... hmm. Maybe vampires could see them by default, because they're technically sort of dead too?
Also, we really do need funeral events and graveyards. Wasn't this supposed to be a game that covered a sim's life from birth to death (and even after that)? There really isn't much to do in the death department yet. How do we not have official funeral events?