If you cast vampiric touch through spectral hand can the temporary hit points gained go to the hand instead of the caster? The hand stores 1d4 of your hit points, it stores a touch spell attack you cast through it until it successfully touches the target. could it also store the received temporary hit points from the vampiric touch making it more durable (with temp hit points) during its duration?
No. The hit points go to the caster. The hand is a spell effect, not a caster.