I would suggest one of the campgrounds near Disneyland, from there you can branch out.
The best time to be on the road is between 9 am and 2 pm, any other time expect traffic.
As far as things to see and do, you could spend a lifetime just visiting attractions in the area. One good source for advice is the people working at whatever campground you stay at.
If you don't have a gps, I would suggest getting one and getting to know it before trying to get around in the LA area.
Come and have a great time and enjoy our weather.