Place to stay advices

Hi,

Appreciate anyone who can help and address my questions below:

Part of our trip itinerary Shirahama -> Kobe -> Okayama -> Hiroshima
We only leaving Shirahama in the evening for 2 nights stay over in Kobe or Okayama.

Need help to decide which location is a better base for us? Prefer to do day trip and avoid too much hotels movement. Plus I'm thinking of shorten the travelling journey back Hiroshima if we stay at Okayama instead of Kobe (we have JR Sanyo-Sanin Area Pas)

Spots we plan to visit in Kobe are
> Kobe habourland
> Mt. Rokko cable car and Shin Kobe Ropeway, (If we only have time for just one, which would you suggest?)
> Kobe Chinatown at night.
It is in June when we visit plus travelling with 3 young children, we will avoid trekking unless it is short and easy route with nice scenic.

Spots we plan to visit in Okayama are
> Grand Seto Bridge via the Seto-Ohashi Line.
> Mt Washuzan Observatory.
(Is this worth visiting?)

We like to sight seeing the Grand Seto Bridge with luggage free, where is ideal train station for us to store our luggages? We have 2 big size luggages plus a stroller.

How about luggages delivery service station to recommend? Can they deliver to our next accommodation in Hiroshima on the same day?

Welcome any suggestions on places we should be visiting instead of what we have planned.

Thank you very much in advance

Between Kobe and Okayama, I don't think it makes too much difference especially since you are buying the train pass to cover the area. True, Okayama is closer to Hiroshima, but once you are on the Shinkansen, it does not matter much (40 min from Okayama vs. 77 min from Shin-Kobe). So I would base the decision on where you might need to take a break (in hotel room) between attractions. Kobe is bigger and things are more spread out, plus you are planning an outing at night, so having a room nearby is convenient.

View from Washuzan is very nice, with the bridges and islands. You can take a bus from Kojima station, and it takes about 30 min. When visiting Okayama, one place I highly recommend is Kurashiki.
https://www.japan-guide.com/e/e5750.html

I have taken a bus on Shimanami-kaido to Ikuchi Island (one next to Innoshima). The view is OK, not that great, since you are on a bus and the bridge segments are short. One thing you can do on the Shimanami-kaido is walk, if you do not ride bicycle. You can also visit the hillside temples in Onomichi, the view from there is very nice. You can hike or ride rope-way to the observation deck there (or ride up and hike down, which is what I did).
https://www.japan-guide.com/e/e3475.html

You seem to be into bridges (I am), so you might also want to consider Akashi strait bridge near Kobe. Take a local train from Kobe to Maiko, and you are at the base of the longest suspension bridge. There is a park and a museum dedicated to the bridge, also.
Video from my recent trip to Maiko: https://youtu.be/RhEhtf_mj6U

Shirahama to Kobe is almost 3 hours with transfers. If leaving Shirahama in evening. I wouldn't wanna go much further than Kobe. As arriving late as it is.