“Bach, Before and Beyond,” a concert series directed by Walter Klauss, will launch its new season on Sunday afternoon at 3 at the Old Whalers Church in Sag Harbor. Mary Hubbell, a soprano, will perform “Bach to Broadway,” a program of music by Bach, Fauré, and Mozart, as well as show tunes by Gershwin, Lerner and Lowe, and Rodgers and Hammerstein.