I have an idea on how to stop your cat biting your hand. The reason why your cat bites your hand might be because he wants to play. Alternatively it might be an aggressive bite as if he is hunting and your hand is prey. This may happen if your cat has just returned from the outside and is in hunting mode and the wild cat in him has come to the fore. Or he might perceive your hand as a source of aggression or a hostile object and attack it.
I think is possible to train a cat to view a person’s hand as something which provides pleasure and therefore not something which should be hunted or the target of an aggressive attack.
If you dangle your hand in front of your cat and in the hand you have a morsel of your cat’s favourite treat your cat will see and smell it. He will perhaps rub his head against your hand in anticipation. You then reward him by placing the treat on the ground or on the countertop in front of him and at the same time use a clicker to reinforce the connection between his friendly behavior (towards your hand) and the reward.
If you do this many times, it is my belief that your cat will associate your hand as an object which brings pleasure and not as an object to attack which should result in no further bites of your hand (unless he tries to grab the food from your hand with his teeth!)
This concept is written on the basis, as mentioned, that your cat is attacking and biting your hand because he perceives it as a prey item. If he sees it as something to play with then this method is less likely to work in my opinion because play is also pleasurable. Under these circumstances the solution is to dangle something other than your hand in front of him to play with!
I would be interested to know what people think of this concept.