I was wondering the same thing. The email they sent me on Feb. 29 said that within the next two weeks they will send me some information about booking a flight, but I haven't heard anything yet. I already booked the hotel room.
I received an email just now from Elena Hillenburg asking me for my banking information so they can set up direct deposit for the stipend.
As far as I know, all that needs to happen for this to be official is the JSPS needs to confirm with my host researcher that he can accommodate me.