What I can pass along is a couple decades working with Japanese businessmen while sitting in the Northwest. (Maybe that's relevant...maybe not.)
There are two boxes on his achievement grid that stand out to me: "being loved by everyone", and "humanity". As Kate points out, there is ample evidence for Seattle being a town that will adore a Japanese star. So I think we've got a great chance there.
But I wonder about the "humanity" thing. From what I know of their culture, this isn't just a description of what someone would like to be...but also what they expect and respect in others. What you say and do--particularly at first sight--is less important than what you DON'T say or do. Silence is valued. Every word is weighed. Which leads me to wonder about JD's approach. He has such a winning personality...and is so conversant with the statistical side...that what he has found works well with American free agents might make opposite impression on someone coming to a new country from Japan. To put this another way, what I presume was Gillick's persona and approach may be far more successful.
There are plenty of people in the M's organization who have been through the Ichiro and Sasaki and Johjima experiences. I hope JD seeks them out.