1: all up to you....not us, find out what root does and why you need it and use it for. Then decide for yourself.
2: always bring a phone back to its original state before you send it in for warranty. They should cover it but as always all cases are different.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?