Sounds like you should stay in Santa Monica like Oski suggested. It fits all 3 of your criteria:

1. All the major rental companies have offices in Santa Monica.
2. The downtown Santa Monica area is pedestrian friendly and has a good amount of restaurants to choose from. It is also next to the pier and beach. Lots to see and experience even at night time.
3. You can get on PCH in the morning directly from Santa Monica once you pick up the rental car and avoid driving in rush hour traffic completely.