Monsterman has skied Japan a few times, I'll give him a shout, he may be able to help. He raves about Japan basically like everyone does because it's usually getting puked on constantly with dry powder blown in from Siberia.
In addition have a look at this Aussie ski forums section on Japan. Register and ask a question or simply spend a few days reading old threads, there is endless good information, probably the best English forum for Japanese skiing info on the web.
http://forums.ski.com.au/xf/forums/japan.51/One thing is for sure, if you go to Niseko you'll find plenty of Aussies there in January, it's our summer school holiday time and plenty of us with kids head to the northern hemisphere in January. Japan is closer than USA/Europe, it's cheaper and is in our same time zone.
I'm in the minority of Aussie skiers, I've not been there yet, +1 likes blue sky skiing, it snows too much in Japan.......
Niseko is on the northern island of Hokkaido, it was the first famed powder destination in Japan, nowadays other ski areas are sort out, probably to avoid all the Aussies that inundated Niseko. Resorts closer to Tokyo on Honshu island and accessed by bullet train are plentiful. Hukuba, Nozawa, Rusutsu, Hakkodo are all talked a lot about these days. And there are plenty of others.
http://forums.ski.com.au/xf/threads/hak ... ney.66840/http://www.powderhounds.com/Japan/Honshu/Hakkoda.aspxAs for gear, I don't know but you might have a bit of trouble finding skinny skis to rent in Japan.
I often read on the Aussie Japan forum about enormous ski gear stores in Tokyo with great prices.