Regarding restaurants, I think you generally get pretty good mileage out of Tabelog. A key problem for short-term visits is that highly-rated restaurants (>= 3.7) tend to fall into two categories: Either the restaurant is cheap and has a long queue outside it (typically things like ramen, but also cheap+good sushi) or it is expensive and requires a reservation. You generally can't just walk into this kind of restaurant unless you get lucky and it just happens to not be fully booked.

Placing a reservation requires a Japanese phone number (which you can get easily for the duration of travel) and most restaurants only accept reservations by phone. Some can be reserved on Tabelog directly, but this also requires a Japanese phone number, and some restaurants will call you back to confirm the reservation, so I'm not sure I would recommend this if you don't speak at least some Japanese. Even if you do reservations by phone, you should expect that most restaurants are already fully booked out for the next week. The best chance to get a reservation are restaurants that are a bit too expensive for their rating.

Ideally you would do reservations before you travel, but I'm not sure what the best way to do that would be in practice.