I agree with the comments above. Especially about Fushimi-inari. Just do it! Go see Osaka castle and skip Himeji. Spend more time in Kyoto ( a day trip is ridiculous) and visit Fushimi-inari, Nara and etc.
You didnt say if you were going with kids or anything ? but i would skip the entire disneyland and disneysea thing. There really isnt anything there worth your time. Your in Japan and you should make the most out of your trip and experience Japan...not disney... If you have kids well...maybe...but i would skip it none the less and spend time where they could experience something japanesse instead.
About Ghibli Museum. You have to purchase tickets in advance, sometimes months before, and it cannot be visited without a reservation. The tickets you biuy will be for a specific date and time. So if you want to see it make sure to get tickets ASAP. I learned it the hard way.
The official site of Ghibli Museum, Mitaka in Japan - TICKETS
Have you already been to Tokyo ? If so i suggest to spend less time there and expend your horizon. I also think 8 nights in Osaka is too much.
heres my suggestion: (oh well here i go again trying to plan a trip) Keep in mind this is only my opinion. At the end of the day your gonna have a nice trip anyway. But heres my opinion none the less. Oh ! and unless your on a very tight backpacking budget theres no reason no to move A LOT MORE.
*** its a absolute MUST SEE!!! You cannot miss this
** very nice! do it
* nice!
everything else is still very worthwhile but those with *stars* are my favorites.
Osaka 4 days/3night:
Nice foods, Aquarium*, Namba*, Castle, etc.
-> 1 day at
Kinosaki onsen town sleep over
move -> Mount Koya stay over night. Perhaps temple lodging*. Oku-no-in graveyard and forest***.
-> Kyoto : 5 days/4 nights
Fushimi-inari***, Kinkaku-Ji**, The Walk of Philosophy**, Kokedera*, Arashiyama** and many more great sights, gardens, museum and area*
then you could go to Tokyo but i would consider a 1 day trip/sleep over to
Takayama to visit the old town* and the Hida no Sato*** village.
on your way to or from tokyo...depending-> Kamakura
to see the great Buddha***
-> Tokyo Xdays/xnights
We all now whats there to see. The possibilities are endless. ***
-> Matsumoto (3 hours from Tokyo)
Museum and castle**
-> Hakone
National parc and Fuji-san view**
You should spend the rest of your time travelling around using Kyoto, Osaka and Tokyo as hubs or discover these towns even more. Maybe climb Fuji if its possible in march/april. Up to you.
Anyway that only my opinion and it pretty much depends of: budget and interest. You dont have to take everything i say but maybe you can get a few ideas out of it. If i could make this trip i would still find a way to do Kamakura, Koya-san, Fushimi-inari and Kyoto.
Have fun planning your trip !!!!!