Kneading is a setback from his kittenhood days where baby cats knead their mother to stimulate milk production and facilitate easier suckling, it's a sign of happiness! Wiggling his bum is oftentimes also part of the same kittenhood behavior. If he's not in pain, there's nothing to worry about with this situation. If the kneading bothers you because of his claws, buy him some soft nail caps to prevent him from scratching you or other people or objects. Please do not declaw him, that is cruel and unneccessary.