I have done the PCH on a bicycle, motorcycle, car and RV. The best month is September as it is dry (relatively), high pressure sets up over the area and visibility is fantastic, temperature highs are moderate and lows mild, and very little fog. And kids are typically back in school. Also, since you asked I would go north to south to keep the ocean on your right and easier to use pullouts. There is lots and lots to see so the very few days you are allocating to the trip will only barely scratch the surface kind of thing.
