It shouldn't be crowded at all. The only day that would be a problem is Saturday. But as long as you avoid that, you shouldn't have any problems at all.
It typically begins to cool down from the summer in October. Still, days should be in the 70's and it probably won't get any colder than high 50's at night. Being in Southern California at that time of year, you probably won't need anything heavier than a light windbreaker (if even that).