How much of his money should the rich person keep for himself, and is it permissible for him to buy a large house, or must he give to the poor and needy?

The wealthy are obligated to pay zakat (definition), and whatever remains after zakat is permissible, even if it is a large amount. It is permissible to buy a large house, while avoiding extravagance, which is forbidden in Islamic law, as Allah Almighty says: "And do not be extravagant. Indeed, He does not like those who are extravagant." It is recommended to give charity to the poor in addition to zakat. It is legally binding to honor guests, aid those in distress, and ensure that a poor beggar is given something.