Welcome to karting! This is an awesome sport, but it can be confusing. I definitely recommend talking to a shop and talking to local racers. MDG Karting in Orange, CA is a great shop that is only a short drive from you. I have known the owner, Stu Hayner, for a long time and he is very passionate about getting new racers into the sport of karting, and keeping them in the sport. He can answer all your questions and also set you up with a good kart that is ready to run for a good price. Check them out at http://mdgkarting.com/.
Have fun and best of luck with your search!