I've ridden from SF to Laguna Beach half a dozen times, always in April. In July, there will be much more traffic, fog and heavy afternoon winds (blowing you south). You will need a mirror so that you can handle RVs, inattentive drivers (watching the view), and the narrow roads along the Big Sur Coast. Frankly, I'd avoid weekends along the Big Sur coast, but many people have ridden during that time and had no problems.
While there aren't any high passes, the road undulates seriously and you will be using low gears every day. There are two dangerous parts. The first is just south of San Francisco is Devil's Slide, a 3 mile section of shoulderless, high speed road between Pacifica and Montera. Since I live in SF, I get my wife to drive me past it. Other ideas are a taxi in Pacifica, a bus that runs in the summer, or taking an alternative route down to, say, Half Moon Bay. Many people ride that section of road, but I haven't and won't. The second dangerous section is through Laguna Beach were there isn't enough asphalt between the parked cars and traffic for a loaded touring bike. On that stretch of road, people have to be careful opening their doors! You can get past some of it by going up a street and riding off PCH.
On my first trip (journal here
), I did 70 mile days as it was too much. I now plan for 50, which I find just right.
On my most recent trip (journal here
), I rode to Santa Cruz, got driven to Carmel and rode south from there (only because I used to live in Santa Cruz and I have done that area extensively).
The LA bike path snakes along the beach and while it can be crowded with roller bladers, joggers, and every other kind of LAer, it is car-free!
You might have to ride on the freeway past Camp Pendleton Marine Base as it is closed to non-military personal. The ride along Highway 5 will not be your favorite but there is a shoulder and it won't be any worse than the 20 miles north of Santa Barbara on the shoulder of Highway 101.
Since you won't be carrying much gear (are you planning on camping?), you will have to be careful in choosing the places you plan to spend the night, especially in Big Sur where the overnight options are camping or expensive and the eating options are limited and expensive.
You might consider couchsurfing.org and warmshowers.org for hosted places to spend the night.
This is one of the world's greatest bike ride. Have a wonderful time.
This is a great bike ride. Have