First of all you're going to want to save up at least 3 grand (rough estimate). Then you will want to search around for cheap flights that you can book as early as possible. How much money you want to save besides what you need for the flight is entirely dependent on what you want to do while you are there. My sensei went to Japan not to long ago to train and he said he spent 1300 on the flight and only spent 400 while he was there. All he did was train though. If you wanted to sight see and shop you would need a lot more. As far as what to bring, it would depend on your personal preference, how long you would like to stay, what is allowed, etc.
Check out this website, it's the tourist site put out by the Japanese foreign affairs dept.:
Japan National Tourist Organization