Can I turn off all "Notification" of all apps, services in Android phone?
Yes, you can turn off all notifications.  Your phone will work fine, but you will not receive any notifications, which will severely limit functionality of applications that depend on notifications to alert you of events and progress.

Furthermore, the amount of battery life saved by doing this will be so close to zero, that I honestly can't recommend it.

Disable notifications for annoying apps.  Leave them on for others.