Yes, online, two days ahead at least or first come first serve the day of. They fill up fast but just watch for cancellations.
South Carlsbad beach is a very enjoyable, popular, well situated location. Get an early reservation. A good base to check out San Diego or its own good place.
Yes, and well in advance
Yes about 6 months ahead if you want to camp in a big group and have all the camps facing the ocean. Even then we were spread out in the park. But we made work and had a blast. Good luck.
Yes. Typically months ahead.
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