I'm looking for recommendations as to which hotels (not considering vacation rentals given the length of our stay) would best suit our requirements:
-- spacious king-bed room or suite
-- ample parking
-- quiet location (or at least quiet room)

Also, we're debating between a walkable downtown location and a beachfront hotel. We prefer easy access to a wide variety of restaurants and shops. Will we feel comfortable walking in the downtown area if we choose that? We'd be traveling in early fall.

I don't know about the accommodations in Half Moon Bay but the downtown is very comfortable and pleasant to stroll through.

Several years ago, pre-pandemic we stayed at the Half Moon Bay Lodge after a weekend wedding in Big Sur. It was midweek in June but pretty warm and so we enjoyed the pool. The hotel was very pleasant and comfortable and offered a nice breakfast included. There was a lot of traffic driving to the town and to the beach but we always found a spot. It was also a comfortable walk.

The downtown area is really nice but I would make sure that there is parking at whatever place you choose to stay.