Till the time battery goes perfect use power saving modeAnd check in safe mode if battery works properly then remove third party apps that is draining ur battery Use less as u can Charge twice a day

So finally u updated congrats For  battery draining It will be resolved within 15-20 days or 1 months automatically because after big update many setups processes etc are taking place so it takes about time to complete U can see after 1 months batte...

Yes we're having 3gb and 4gb ram so suitable is available

Nothing will delete everything will be as it is just features change

Yes