Help for a Nashville/San Francisco/San Diego Trip?

I plan on leaving Nashville, TN on June 10th to San Francisco and fly back out of San Francisco on June 18th. The plan is to rent a car in San Francisco and take my time to drive down the Coastal Highway to San Diego. I want to see as much nature/culture as possible and explore. Along the way I want to spend some time at the beach/beaches and see some local history. At San Diego I want to go to the zoo. I plan to stay at hostels/airbnb along the route. Once I leave San Diego I want to drive the fastest route back to San Francisco, return my rental and head home. Does anybody have any recommendations on where to stay, what to do/eat and any issues I might come across? Also, does anybody have any suggestions on tweaks I can make to my plans? I am very open as this is my first time to California. I am planning on spending $500 for the round trip flight, $500 for lodging and $500 for gas, food and anything I want to buy or do. All my essential stuff will fit into a backpack so I will only have 1 bag to worry about.
8 mo
I asked some similar questions, but this one addresses more concerns I just thought about. Any info would be appreciated.
Help for a Nashville/San Francisco/San Diego Trip?
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