I must confess that I dont know Nagoya very well, so I cant help with local hobby shops. In terms of things to bring, Id say:
two
tape measures with inches on them. You cannot buy these in japan.
paintbrushes, and backup paintbrushes. These are also hard to buy here. Paint isnt so much of a problem though.
green stuff/grey stuff/brown stuff
blu-tac. I dunno if they have this where you are. Its British, I think. Anyway. Its a temporary putty used for sticking posters of pop stars to teenage children's walls, mostly
Gamers use it for holding things while glue dries, and also for temporary stuff like holding weapons on tank cupolas and whatnot. Its also useful when youre pinning stuff.
your mini collection, obviously.
a
credit card: this will allow you to buy things from overseas for far, far less than you would otherwise pay for them in japan, even if you count the shipping costs.
I dont know how easy it is to pursue a gaming hobby where you are, but here it can be a bit tricky. Be prepared to travel for games, even outwith nagoya. Personally I commute about an hour and a half for my games most times. Sometimes more, sometimes a bit less. Bearing this is mind you'll want to have something that you can use to conveniently transport your minis from place to place. You will probably be travelling by train, as the train network here is very, very extensive.
btw, in terms of minis to bring, popular games round here are: warhammer fantasy, warhammer 40k, warmachine/hordes (a lot of japanese players play these), and Flames of War. A few of us also play Malifaux and Uncharted Seas. the GW specialist games also have a following, though we havent played much recently (Blood Bowl, Mordheim, Necromunda)
Also, on a non-hobby note, it is well worth your time to learn how to read Katakana and Hiragana if possible. These aint too hard. If youre feeling brave, make a start on Kanji too. Dont be intimidated by the lingo/writing system. If a 2 year old japanese kid can speak it, so can you, desho? Even learning only katakana and hiragana will make your life much, much easier, and you can do it in a coupla weeks, maybe a month or so.
anyway, if you have any other questions, just ask. Im sure Mike and Primarch will be able to advise on life in Nagoya, as they both live around there.
. For the average painter, good quality bushes, paints and other modeling supplies are readily available. Japan is the home of Tamiya after all. And as Primarch said, Vallejo paints are also available in Nagoya too. 