Pretty much everything
@kvetcha said.
In addition, the first part of the culture shock when you touch down will be the sound of your own voice. You'll realize that you, as an American speak VERY LOUDLY whether you knew it or not. You'll quickly adjust your average speaking volume and when you touch back down in the US you'll experience some reverse culture shock as you wonder why tf everyone is yelling all the time. LOL
Having conversational Japanese at your disposal will make many things very enjoyable for you. Average conversations with curious locals will go much more smoothly. I really wish I understood everything of what my new Yakuza friend was saying when I went drinking with him in Golden Gai. We compared tattoos and he seemed pleased but really I only caught maybe every fourth thing he said, at best.
As far as a daily budget, it will fluctuate a bit depending on the city and the types of things you like to do. As Kvetcha said, food is mostly very affordable and I you wouldn't need to budget more than $40-$50 per person per day if you wanted a nice dinner at the end of every day. You COULD go to the super fancy restaurants and spend a mint but really, why would you? All the best spots are so affordable you'll wonder how you ever spent $20 on a freakin' burger over here. I would say, if you are a foodie at all look up one of the high-end restaurants and make reservations if you can. But really, only do that once. The level and quality of food in pretty much all of Japan is breathtaking.
In terms of spending, well that's going to fluctuate quite a bit depending on your preference. I had originally budgeted $200 per day for shopping, entry into places, etc. The first week of the first trip I blew past that budgeted amount by a wide margin. But that was because I was like a kid in a candy store. By week 2 I was staying well below that to see the things I wanted to see. And by week 3 (I was in rural Japan) that budgeted amount seemed laughable. I barely spent money that last week. So really, what are some of the things you'll want to do while there?