I'm pretty sure California has the same 3 foot law that we have in Nevada. Cars are supposed to give you that amount of passing room. Riding on the sidewalk is really dangerous. Go to the first forum at this site (Advocacy and Safety) and read the comments from avid cyclists about riding on the sidewalk. Once you ride for a while you will learn which streets are safest and which to avoid. It's better to go a little out of the way than to ride a really horrible street. Yes, you are supposed to ride to the left of parked cars allowing enough space so you don't get doored.

Don't change anything on your current bike unless it begins to malfunction The parts are "entry level" which means they might not work as was well as high quality parts but they should work.