I know it's too late for the OP, but I wanted to offer my advice since I traveled around Japan a lot in the 2 years I lived there. You really don't need to book restaurants unless it's a very fancy place (which I stayed away from). Just look around at all the various mom-n-pop restaurants, look at the plastic replica menus in the window, smell the aroma, see if it looks like they are fairly busy, and ultimately just go with your gut and choose a place. I was almost never disappointed when I did this. Generally, the quality of the food is very high even in inexpensive family restaurants, and you can find some real hidden gems that may not look like much outside but have excellent food. You might also try asking locals where is a good place to eat that isn't too expensive... I discovered some out of the way places that became some of my favorite restaurants that way.