Disable People: Settings -> Apps -> ALL -> Contacts, and then select disable
However, the people app is your contact book. The one you can access via phone app is only contacts with phone numbers, and you cannot see email. I don't think you should disable contacts. You can download some other contact management app, I suppose.
You can surely disable Music and others that you feel are running too much in the background and you don't use
It is also odd that you are still on 4.0.1. I don't like the fact that we don't have 4.0.3, but you probably should go to Settings -> System Updates to manually check for 4.0.2
I got my phone around 9:30am 15th, and update came through around 10:30am 15th...
Not much I can say about battery life. More we can do with our phones, less battery life we can squeeze out. 4G, NFC, Large Bright screen, sync everything, play games etc etc
It is, again, very odd that your OS takes most battery life. Usually it's display, and win by a large margin. There are speculations about some phones are not sleeping when they are supposed to, but no consistent patterns found, even in small scale experiments.