As for whether Kira was the same person as Light, it depends on how one defines "Kira". On the one hand, Kira was the name given to the vigilante who used the Death Note to kill criminals. In this sense, Light and Kira were one and the same. However, Light also had a dual personality that emerged after he made contact with the Death Note, which could be seen as a separate entity. This aspect of Light was ruthless, cunning, and willing to do whatever it took to achieve his goals, even if it meant sacrificing the lives of others.
Therefore, while Light Yagami and Kira shared a physical form, they can be considered separate personalities or identities.