Does a Kuei-Jin drink someone's chi from their blood like a western vampire, or are there other methods?
They can feed on (depending on their dharma level) flesh, blood, breath and eventually on the ambient chi of the universe (source). The lower level of dharma, the more "monstrous" way of feeding is required (so with very low dharma you have to eat corpses).
If you like some homebrew rules extending those, please check this page