The reasons for using f11 & f16 is to get a larger depth of field throughout the whole photo. The nearer objects like maybe a meter away from you will be clear at around f8 - f11. Another reason for using f11 is to have the starburst effect on the street lamps and lights. at wider aperture, the starbursts will look different or maybe it will just look like a glowing ball. Another reason for using narrow aperture is because I want a longer exposure for the trailing lights of the cars. If by using a much narrow aperture like f16 - f22, the depth of field will increase but will cause the images to be less sharp.
Yes, you are correct. If all other settings remain, and you use a wider aperture, the result will be an overexposed pic and cannot be corrected later. Details might also be lost.
