Mobal eSIM. Install it at home, switch it on after landing at Haneda.
Suica or Pasmo in Apple Wallet for metro and local JR. Buy the three Shinkansen legs on the SmartEX app.
WhatsApp for the group chat. LINE for restaurants, hotels and locals.
Early-to-mid March is before peak sakura. Expect plum blossoms and early kawazu-zakura.
Shinkansen oversize bags need a reserved seat with luggage space. Or send bags ahead with Yamato.
Check opening hours a week before. Tap any stop name to open it in Google Maps.