You have 3 stations to choose from.
Esplanade. Located on the Northern tip of Chowringhee, near the Oberoi hotel. Convenient for visiting the Birla museum.
Chandni Chowk. Good access to Dalhousie Square.
Central. Located just outside College Street and the Calcutta University.
As Esplanade is very central buses from all over the city are going here frequently.