However, using very small aperture at night requires you slow down the shutter speed in order to capture enough light in the scene. Hence, at iso 200, 5 minutes exposure was used. With this setting, water was beautifully smooth like a big mirror, reflecting light from Harbour bridge and the city.
Unfortunately, the moon and stars were also affected from slow shutter speed. Five-minute exposure was too long to capture standstill moon and stars.Theoretically, a veteran photographer told me that the maximum exposure we can use without getting star tails is 600/focal length (e.g., 600/21mm => 28 seconds). Hence, I separately took a photo of the moon and star by 15 second, f16.0, and iso1600 so that they wouldn't move in the scene.
Later, these two photos were blended in Photoshop by using layer mask technique and changing the layer mode of the moon and stars to 'Lighten'