Flights to and from America have a 60 kg or so weight limit, with any additional baggage racking up a fairly nominal extra charge. Sending your winter clothes by sea mail is by far the best bet. It is slow but reliable and cheap. The average package takes about 6 weeks to 2 months so pack ahead of time. Rain gear is also essential.
Japan can get very wet at times.
If you can spend the money, pick up a nice pair of Gortex hiking boots or some other kind of all-weather shoe. Unless you get a car, you will probably be biking, so you are going to need a nice rain suit. And I have a North Face Gortex windbreaker with a nice hood. If you are used to a fancy kitchen, stocked with all the items you need to create that special dish, you need to do some serious unlearning. Most kitchens in Japan don't even have a stove.