mobile

Hello XDA Community,
I have purchased a Note 4 recently and it is a great device. I had a S5 before, as I got after my upgrade, but got this phone as a gift. I was thinking about selling the phone and keeping the money, but decided to keep the phone and sell the S5 instead. The phone performs great and has lots of storage. The only problem I have is after using it for a while now, I found it very slow. Since this has 3 gigs of ram, I though it would be faster than my S5, which was slow occasionally. I feel reluctant to sell this phone, but forgot the reason why I purchased the phone was because of its IP67 certification (my S3 got water damaged :( ) and was a fine size for me (have small hands). My questions are:
Has anyone encountered slow/choppy experiences with this device (Note 4)?
Is there any program to back up the phone (like all the data, like an iOS backup)?
Does rooting actually void the warranty and you can't retrieve it back (Note 4)?
Is there any way I can extend the internal storage of the S5 with an SD Card (without rooting), so I can store apps and such on there. (I have tried App2SD/Move the SD Card, but I want to use the SD Card as an internal storage device)