Greetings and welcome to BYC. Glad you joined. Congrats on your about to start chicken adventure! If you don't want the extras, order by phone and make sure that they don't include any. Whether they'll be safe depends on where you are in CA. Mountains? Coast? North/South? Early/late May? Location makes a huge difference too. (that being said, please put your location in your profile. Old folks like me will never remember your first post

)
Chicks are packed with a (water) gel pack so they can drink in shipment. They can normally survive for 3-5 days with no problem during shipment. They can and do die for any number of reasons. The shipment could get delayed or "lost". It might sit overnight in a truck in a cold location like the mountains during travel. The hatcheries can't do physicals on every chick they ship and some are just not healthy internally and fail to thrive or die during or right after shipping. They can get injured during shipping.
Even after you've owned them for a while, things just happen. One might have a heart condition, or some other genetic issue that causes death. They can catch diseases that can kill them. They could get killed by stray dogs, your neighbor's dogs, YOUR dogs, or any of a host of predators that love chicken dinners. And in the end, they will all die as that's how life works and always ends. The average life for a large fowl chicken is 4-6 years. Of course there are always a few that live to be 25

, but that's not "average".
So anyway, there's a wealth of info, knowledge, and experience shared here. Also, great folks eager to help others with a problem. Browse around and learn what you can. Post when you have questions. And above all, make yourself at home!