[Firebird]

For a whole year i would go with a apartment as well. If you are in the area of a big city the apartment will be expensive, but so will the hostel. And staying for a year in a hostel will most probably not be cheaper than an apartment.
If you end up outside the big citys you can easily rent a normal sized apartmenr with the salary of a english teacher. If you are in big citys the alternative to an apartment might be a gaijin house or shared house. Its a little bit like a hostel just that everyone gets their own room and shares shower and kitchen (often living area as well). The advantedge to a hostel is that if you want to be alone, you can easily seperate yourself from the other housemates and if you want to chat you can just hang out in the living room.
I did live in such a place for 2 month in Tokyo (Oakhouse was the company) and i did have a great time! I ended up making many friends (mainly japanese) and having a great christmas party there.

Some schools might offer you help with finding acomodation.