Software update removal

FYI. Apple does not support downgrading iOS versions. In addition, Apple stops signing the earlier release at around a week after a new update is released. However, if you still want to attempt this, just perform an Internet search on "how to downgrade iOS on an iPhone," and it should result in a number of articles for you to review to see what it entails.

You can't - but is it normal for high battery use for some hours after an update, while the phone gets everything set up.

Nothing but security features in 14.4.1.

Nothing that changes anything regarding the battery.