When to reserve train tickets

Are advanced reservations generally required? We are travelling in May and taking the train from Kanazawa-Kyoto, Kyoto-Hiroshima, and Hiroshima-Fukuoka. Should I book all my train tickets when I arrive, the day before, the day of...? What about day trips from Tokyo to Nikko and Kyoto to Nara? Thanks

Are advanced reservations generally required?

No, they are generally not required. Only a small number of trains requires seat reservations, e.g. night trains and some of the shinkansen heading north.

We are travelling in May and taking the train from Kanazawa-Kyoto, Kyoto-Hiroshima, and Hiroshima-Fukuoka. Should I book all my train tickets when I arrive, the day before, the day of...?

If you know exactly in advance which trains you will take on what day, I would make the reservations a few days in advance. But if you prefer to remain flexible regarding specific departure times, I would wait and make reservations later. It also depends on whether you travel during a busy travel period or not.

What about day trips from Tokyo to Nikko and Kyoto to Nara?

It depends on which train you are taking. Limited express trains by Kintetsu and Tobu do require seat reservations, but all others do not. For local and rapid trains (and Kintetsu express trains) between these destinations, seat reservations are not even possible.