Temperate Climate Chipilin?

I'm at an urban permaculture farm in Roanoke, VA and writing to see if anyone has experience with or knowledge about growing Chipilin (Crotalaria longirostrata) as an annual in temperate climates. I learned about this plant in Guatemala, where it is used as a perennial nitrogen fixer and edible shrub. Also a traditional ingredient in Pupusas from El Salvador! It's been pretty hard for me to find info on growing this, the best I've found is: http://www.growingmagazine.com/print-5120.aspx

I have some heathy, young chipilin plants but am not sure the best way to grow this as an annual, can anyone help me out?

A number of questions:

How should I care for it besides putting it in decent soil and keeping it well-watered?
Could it become invasive?
Why is seed so expensive?
Will I be able to save seed in USDA zone 7?

Thanks y'all!

UMass/University of Massachusetts grew these in a much cooler zone.

See also: https://www.wpi.edu/Pubs/E-project/Available/E-project-042810-163614/unrestricted/Bisson.Mason._Identification_of_Rhizobia_Species_That_can_Establish_Nitrogen-Fixing_Nodules_in_Crotalia_Longirostrata.pdf

If you can translate this one there is some good information to be learned. http://biblioteca.usac.edu.gt/tesis/01/01_1225.pdf (Note that one of the types listed is not Crotalaria longirostrata but is Crotalaria vitellina.

I am in zone 8 and my neighbor grows Chipilin in the family veggie garden. Saves seeds. Due to the unusually cold weather these plants died back early this past winter but enough seeds was saved to start a new crop.

Whichever method you use to grow tomato from seed I would suggust using that method for the Chipilin to get an early start due to the shorter season.

Alternately, you could winter-sow some seeds and let the seeds decide what is best.

Good luck.

Alan Bergo just got me interested in this plant!  Anyone growing this in zone 5 or 6?