As seen by me in Nagahama, Japan:
Not a willow, is it? Never seenn a willow with anything else then obscure white/green flowers
I do not understand why willow would die in a mild winter. Certainly not if you gotthe cuttings there. I would however recommend not even starting, and working with a species that is more suited. Working on a specific plant or species just "because it is available" makes for long roads to mediocre trees. Spend your time and energy on plants that are better suited and on the long run have more satisfaction, I would say.