Get a grad degree now. If you go into the english teaching thing in japan that so manyt do, it's going to be tough to go back to school after.
In regards to going to japan and coming back having saved money don't. Nobody actually saves money on these things. For every person that comes back with savings you've got 10 who spent all of it. That's just how it goes. You could go there for a while, but I'd tell you to get your graduate degree first. Of course I don't know what a grad degree in liberal arts is worth 🙂