help please! got the job, what else do i need..?

hi there,
i just received a pending offer for a job position in the states (im currently in canada)
what i've got so far is:
-MN license
-Endorsed for temp license to NC
-Visa Screen Certificate
-in the process of completing required documents from the hospital

what else is needed?
I think I still need the official letter to bring with me once I try to re-enter the US.
I was told I need to apply for work authorization with USCIS? Is this is I-765? If I read correctly that application also requires photo/fingerprints and the fingerprinting can only be done at authorized places that seem to only be located in the states????
I'm really confused about that part so if anyone can offer some guidance, I'd very much appreciate it.

I also heard that the TN visa is now for 3 years, not just 1. Is this true??