You should have plenty of ventilation. I have plenty of ventilation with my window closed but I like the extra summer ventilation it gives when open. I also prefer the light that it lets in.
If you don't have a window you will get poor egg production, especially in the darker 6 months of the year. You need ventilation anyhow (like a REASONABLE amount of ventilation, not just a coupla tiny airholes) so far and away the simplest thing is to make a clear plastic panel that hinges or slides down as a cover for the vents. When it's nice weather you leave it open, and the light and air come in thru the (hardware-cloth screened) vents; and on the few occasions when it's temporarily so windy/rainy that you close one of the vents, light still comes in thru the clear cover.
It depends somewhat on how big your coop is, but if it is, say, 4x4' for four hens, you want something like A MINIMUM OF two 1x1' or 1x2' windows/vents.