I must humbly state my opinion. I too will be moving to Japan soon and have informed myself as well as possible with former students from there. I was told by the great majority that Hombu Dojo isn't quite as mystical as it is made out to be. You show up, pay, train like a madman, and go home. The idea of going with a white belt is always good. I'm inclined to believe that the situation described by our friend BC is an acception to the norm. Oh, and a practical Japanese language course might be helpful too, I've found it to be for myself anyway.
At your service,