>> Century Hotel Southern Tower for the one night in Tokyo ... Yes, I know it means schlepping bags for just one night.

Taxi. 7USD.

>> feedback on green car on that route? Is it much of an upgrade?

no. Slightly wider seat.

>>Shinkansen all the way to Hiroshima from Tokyo .... but it's likely I'll have all my bags with me

Use luggage delivery between hotels, and you only carry a day bag. That's how Japanese travel.