Some thoughts: Nacimiento-Ferguson Road is a gnarly climb! Highway 46 from south of Cambria to just south of Paso Robles proper is a much more friendly hill. It has a nice shoulder and the grade isn't so steep. It's still a long climb though.
Paso Robles (and King City and Atascadero - anyplace inland) will be HOT in July. Temperatures over 100 degrees are fairly normal.
Riding down the coast from San Francisco is an epic ride - stunningly beautiful! It's not flat though - lots of ups and downs. There's not much shoulder in many places, and there can be a lot of traffic. Camping is easy, at least south of Monterey (with which I'm most familiar.) There's Pfeiffer Big Sur (with hiker/biker spots, a store, and a restaurant), Kirk Creek (beautiful hiker/biker spots in the woods overlooking the ocean), San Simeon State Park (just south of Hearst Castle and just north of Cambria with all its shops, restaurants, groceries, etc.), and Morro Bay State Park. San Luis Obispo has an Amtrak station which will box your bikes.
Another option might be to take the train down to San Luis Obispo, stay in a nice motel/bed-and-breakfast, and do some day loops. There are plenty of wonderful rides (go to
www.slobc.org and look for routes.) Then you could ride down to Solvang, get another room, and do some loops. There's a bike tour company that sells packages from Solvang. You could do it without paying (except for your room.)
Just some random thoughts.