Assistant Professor position is a secured job for at least 5 years, with a much better future. Go for it. Even you apply for NIW, 5 years is long enough to get a GC in such a stable position. Once you sub-mit NIW by 6th year, you should be able to extend H1.
You can always negotiate with the school at your second year and seek for sponsorship for greencard when you get more fundings. School likes to keep you as they want to retain ~50% of income from the fundings.
So, don't worry.
