I usually plan my trips to Japan on relatively short notice - currently looking at March - accommodations will be available for the Spring though may be harder to find in heavily touristed areas such as Kyoto.
End of April, beginning of May is Golden Week - three closely space holidays so a tough time to travel and find accommodations but outside of that finding hotels should be doable.
Consider using the Japan Digital Entry site to ease your entry into the country: https://services.digital.go.jp/en/visit-japan-web/
You will get a QR code for your phone and that will speed you through the process.
A Suica card - https://www.jreast.co.jp/multi/en/welcomesuica/with_ic_special_pass.html - is a handy way to pay - just tap and go. Can be used on trains, subways, convenience stores and many other locations. The Welcome Card expires so I now use the Suica app on my phone rather than the card. Easy to use and easy to reload. In one instance my wife realized her eSuica did not have enough money to pay for her train ride so she reloaded it on the spot. The hard cards can be reloaded as well but only at certain JR stations.
We purchase eSims for our phones and that makes things easy for travel for us.
HIroshima - Kyoto - Tokyo is a lot of ground to cover in that short a time. Doable but you will spend a lot of time traveling. Though transit is Japan is so good that will not be unpleasant.
And while credit cards are easy to use, we still found cash handy in some places and at odd times. The ferry from Shikoku to the art island of Naoshima was cash only when we traveled there this past November. Ran into a few other cash only spots though that is more likely if you are off the beaten path so to speak. Easy enough to get cash at an ATM if needed.
Have fun. Japan has become my favorite place to travel - clean, safe, easy to get around and generally very nice people. (When my wife dropped 20,000 (roughly $US150) on the ground pulling something out of her pocket we only discovered it when someone came running down the street after us to give it to her. And we seem to have gotten somewhat old and gray and so people constantly try to help us. In Osaka, one woman insisted on carrying my wife's bag up the stairs at the train station!)