You have asked far more than the one question that you are allowed to ask, so I have edited it down. In responding to this question I will comment on a few aspects of the religion of the Na'vi as presented in the film so you can go back, watch the film again and develop my initial ideas.
Certainly the major aspect of their religion that you need to be aware of is the closeness of their culture and society to Nature and their world. In a sense, I think Cameron was making a parallel between the Na'vi and so many other indigenous people groups, who may be considered "uncivilised" in terms of their lack of technology, but show themselves far more able to live in harmony with nature.
Note the following aspects. When Neytiri saves Jake from being killed in the woods at the beginning, she says a prayer of release for the creature that she kills. The Na'vi are a people group that do not kill and slaughter indiscriminately. They only hunt what they need and say a prayer of release for all that they kill. In addition, note the importance of sacred trees and groves to their religion, and the absolute grief that is shown when one of their ancient holy sites is destroyed. The Na'vi have a completely different outlook on nature - they do not see it as something for them to treat as they want, rather they shape their lives to live in harmony with it and build their lives around it. You will also want to comment on the deep connection that there is between the Na'vi and the animals and the whole planet itself - living in harmony with nature obviously has massive benefits.
Hopefully this will get you started on this very interesting assignment. Good luck!