If you plan to sleep in a tent during a multiple-day cycling adventure, one of the major challenges is finding a place to shower. The ubiquity of public bath houses (onsen or sento) in Japan made it easy for us to clean up almost every day of our ride without needing to get a hotel room.
There are hundreds of government-designated rest stops throughout Japan called Roadside Stations (michi no eki), which came in handy on our ride. They typically have information on the local area, food and places to rest. Some include playgrounds, an onsen and other family-friendly attractions.
If you arrive by bike in a town without any advanced information, make your way to the main train station. That is typically where you will find tourist info. Police officers, often stationed in neighborhood "police boxes" called koban also usually have helpful information.