*sigh* Coming back broke really can't be helped eh... xD for my school trip I spent around $600-$700 and that was in 18 days... :O but there was this one guy who was really stingy and scabbed money off the teachers x| I wonder if he'll ever pay them back... ^^;
Aah, memories...
Your plan sounds really fantastic!! You should be all set to go with your Japanese skill, I mean, I don't know if you've done any Japanese proficiency tests, but I haven't done any and I was fine...! What's more is that you learn new stuff while you're there, so it's great!
You must go to a kareoke bar... XD okay, not must, but it's a recommendation!! I mean, they're SO much fun!! And they have tons of english songs (a whole book/menu of them) to choose from, so you guys'll be a-okay~
Onsens and temples and all that traditional stuff is pretty amazing too!! Festivals are also TONS of fun
And of course, you can't not go shopping... try Aeon if you can find it. The place I went to was MASSIVE. :O
AND VENDING MACHINES
you can't miss them... I mean, they're EVERYWHERE. You wouldn't believe some of the stuff they sell in them... xD
Okay, I've rambled too much... but I hope you have tons of fun!!