Hello! Robert here. I left Japan two years ago but I'm still in touch with folks in Nagoya.
When I first arrived in Japan, I experienced what could only be called a baggage nightmare. Not only was I over-burdened with bags during my stay in Tokyo, but I suffered insupportably at the hands of the mid-Japanese summer. It was about 100 degrees Fahrenheit (38 Celsius) with a humidity level hovering around 95%. And to add flame to the fire, many buildings (including many parts of Narita, many government offices, and many private homes) are not air-conditioned. It's been two years since, and I still have nightmares.
I arrived in Tokyo with a pull along carry-on, a garment bag, and a good-sized sac de voyage, all of which were filled to capacity. Fearing that my other luggage would be delayed in arriving to Nagoya, I took the precaution of keeping 2 (or more) weeks worth of stuff with me. HUGE MISTAKE! I found myself riding buses with bags on my lap, walking from the hotel to the subway station in the sweltering heat with bags in tow (I arrived soaked in my own sweat), and desperate to get some of the scarce luggage space on the Shinkansen. All this personal torture, ironically, ended when I collected the rest of my baggage when I arrived the same day in Nagoya. So, be forewarned! Take ONLY the essentials to the Keio Plaza (suits, toiletries, evening wear).
In packing up your affairs, you might want to also keep in mind the following information. As I'm sure you're all aware of, JET guidelines specify ceilings on baggage allowance. However, as was the case with most of us, airlines tend to be quite lenient when calculating business class weight limits without extra charges (I was allowed 85 kilos). So, if you are really keen on bringing over most of your stuff from the start, don't stress out about over-packing, but please take some precautions.
When packing, arrange your essentials (toiletries, summer clothing, host family gifts, etc.) in the same suitcase(s). In the case that your airline does not permit excess baggage without charge, this will allow you to make a stress-free decision on which bags to take and which to leave behind with family or friends at the airport (who then can ship your stuff to Japan later). Another good idea would be to make it to the airport early in order to check-in before the airline staff get bitchy and decide not to let the excess baggage slide by. If you are lucky enough to have everything flown over, be sure to send ALL but one small piece to Nagoya! And finally, you may just want to bring over your summer/fall essentials and have everything else shipped to you at a later date. It may seem expensive now, but once you're here and on salary you'll find it's nothing. If I had to do all this again, I'd definitely ship most of my junk and bring over the important items only. (If you are considering shipping some of your things to Nagoya, check the contact page for more information.)
Good luck,
Robert
Saskatchewan, Canada