^ AFAIK, N9000 is the regular one. N9002 is the dual-sim one. N9005 is the LTE 4G one.
Unless you have a Zong Sim Card and plan to use it's 4G service in future, you won't need the 4G capable one.
As for root, think of it as like admin access on your windows PC. Some specific apps need that admin access to perform their task.
If you're a casual user, you likely won't need a rooted phone. If you are a technical user, then root access may be useful to you.
If the pre-rooted one doesn't come with warranty then don't go for it. You can easily root the non-rooted one and unroot it when/if you need to claim warranty.