>> from Hiroshima port to Matsuyama then couple of nights in the area and visit Takamatsu before the train back to Okayama/Kobe/Osaka

Matsuyama is where I fell in love with Japan. It was ephiphanous. That was in 2001 on my first trip to Japan. I very much liked my stay at Hotel Patio Dogo which is basically across the street from Dogo Onsen (famous, historic, must visit).

Am not sure of your routing now. Matsuyama would fit where Himeji is in the itinerary in your OP. Route from Kyoto would be shinkansen to Okayama then a l'ex across the Seto Ohashi Bridges (very cool) to Shikoku and on to Matsuyama. Do that trip in daylight. I crossed the bridge at sunset and the views of the Seto Nai Kai and islands was stunning (but then it was dark on the Shikoku part of the ride).

Then go from Matsuyama to Hiroshima on the fast boat (at sunset).

I enjoy visiting Fukuoka. Not a fan of the Hilton location unless going to a Hawks baseball game. I very highly recommend going to a game even if you are not a baseball fan. You want to sit in right field. Not being a baseball fan is not a reason not to go to a game. It is fun and something of a cultural experience, real Japan.

Nikko was annoyingly busy with foreign tourists when I finally visited there in November 2019. It was just too much and I was disappointed.