It sounds like a fun trip!
I have made a bunch of 800+ mile trips in my '99 Boxster with no problems, so you should be fine. You don't say if you just want to stay in SoCal, but if you want to see redwoods you are going to have to go farther north than San Diego, the closest ones are at Sequoia National Park. I would also highly recommend cruising down Pacific Coast Highway in San Diego, and I enjoy PCH through Corona del Mar. I've been here so long, I don't think like a tourist, so the only things I can think of to do would be see the beach, drive down PCH, get an In-N-Out Burger, and enjoy the sun.
