You should indicate if you accept the admission offer. To complete the acceptance of admission offer, please settle the deposit by the payment due date stated on Admission Notification.
Then, please follow the steps in How to Register? to register provisionally. In such a situation, your student status is not yet confirmed and you will NOT be allowed to commence to study until you have fulfilled all the condition(s) by the deadline stipulated on the Admission Notification.
Yes, you have to apply a new student visa.
No, you don't have to apply for a student visa, but you have to present your employment visa to the Graduate School as soon as you receive the admission offer. Please make sure your visa is valid during the entire study period.