Your itinerary (as is initially shown) sounds good, on the whole,
but not yet well organized.
For some parts of the itinerary, your timeline sounds hectic.
I recommend
you check the cancelation policy of your already-booked accommodations.
If you still can change or cancel the bookings free of fees or at a low cost,
it should be better to improve the order of your destinations.
For your Hiroshima + Miyajima trip,
I wonder why you will start not from Osaka (City) but from Mount Koya.
(Maybe it is hard to change the booking of your Mount Koya accommodation.)
It takes about 4 hours
to go by (cable car and) railway from Koyasan Station to Hiroshima Station,
which sounds time-consuming to do in the morning.
Also, in November 2018,
for you to watch the torii (gate) of Itsukushima Shrine on different backgrounds,
compared to the 11th and the 12th,
the tidal condition seems better on the 8th and the 9th.
On each of the two days there is expected a great range of tides,
a high tide in the morning and a low tide in the afternoon.
A one-day round trip from Osaka to Okayama, Kurashiki and Himeji sounds too packed.
On your way from Miyajima Island to Kyoto (City),
you can stop by or stay overnight in Kurashiki, Okayama (City), Himeji and Kobe.
head to Himeji to see the castle before it closes Would you climb the donjon and see the interior?
Then, considering possible crowdedness,
I recommend you get to the castle in the early morning, especially on a weekend.
(The main keep was renovated in recent years until 2014.)
There are slopes on the way to the castle and some steep staircases inside the donjon.
You might hope to visit also the nearby garden.
https://www.japan-guide.com/e/e3502.htmlI bought a JR west pass (Sanyo Sanin) for this trip Why did you choose the (7-day) Sanyo-San'in Area Pass?
The usage area of the (5-day) Kansai-Hiroshima Area Pass
is enough for trips to your now-planned destinations other than Mount Koya.
https://www.westjr.co.jp/global/en/ticket/pass/kansai_hiroshima/A major difference other than the duration and the railway scope of validity is,
when your seat is reserved in a Limited Express or Sanyo Shinkansen train,
the Sanyo-San'in Area Pass covers the surcharges,
and the Kansai-Hiroshima Area Pass does not cover them.
These JR-West passes are not valid on the Tokaido Shinkansen
(Shin-Osaka -- Kyoto -- Nagoya -- Shin-Yokohama -- Tokyo),
which is operated by JR-Central.
When you go with your JR-West pass
past Shin-Osaka on a Nozomi or Hikari train to Kyoto,
you have to pay the basic fare and the Shinkansen surcharge
separately for Shin-Osaka -- Kyoto.
Maybe you are aware of this, but Mount Koya is not served by JR.
(You now plan to spend some hours with your JR-West pass valid but not usable.)
can I go to Uji from Nara on my day trip? That depends on which sites you go around.
I suppose
Byodoin Temple in Uji City
and Todaiji Temple + Kofukuji Temple + Kasuga Taisha Shrine in Nara City
can be visited in a one-day trip from Osaka City.
When you add a site in another area (e.g. Horyuji Temple),
it may be better to stay overnight.