Kaltxì ulte zola'u nìprrte' ma Rhaitus!
It's nice that someone come here just not only because of film but also because of culture.
As for language, in the beginners section are enough good and helpfull thread/articles.
As for culture, we know 'some' but we expect more from next movies.
Although i know something, there is only one people that can you help the most, she call herself Neytiri because she is one of the best Na'vi speaker who also know lots of culture-releted thing.
She collected all culture thing into one PDF document.
If you want more or have any questions, feel free to post them... Edit: links are in spoiler
So, here is her Keypuk account
And here is the PDF