Thanksnwill keep in mind that there are options available

Lots of good advice so far.

For ryokan with onsen, consider Hakone. But keep in mind that onsen ryokans have lower rates Sun-Thu nights and many places don't start accepting reservations until 3-6 months out.

You might do something like this:
nights of 3/23-25: stay Tokyo (gives you 2 full days in Tokyo)
night of 3/26: spend the day sightseeing Hakone, then check into ryokan in Hakone
nights of 3/27-29: stay in Kyoto (gives you 2 full days of sightseeing in Kyoto)
nights of 3/30-4/1: Okinawa (2 full days to see Okinawa)

There are a couple dozen temples that take overnight guests, and there's a central booking office for them. You arrive at the top of the mountain via funicular, go to the booking office, and they give you your temple assignment.

It's like staying in a ryokan, except that you will be served only vegan food and will be expected to join the 6:00AM service with the monks. (It involves listening to them chant sutras in classical Chinese.)

After breakfast, you can walk the forested path that leads to the grave of Kukai (Kobo Daishi). The path is lined with the graves of famous figures from Japanese history, because Shingon Buddhists believe that Kobo Daishi will return, and prominent people continue to pay big money to be buried near him. The modern part of the cemetery can be rather amusing, because a lot of their "inhabitants" are major industrialists whose gravestones signify their industry.

Great advice above.
One thing to consider if you wanted to move your schedule around is that the end of the March Sumo tournament in Osaka is March 25. That is the most popular day, so if you really wanted to go you'd be better off trying for March 24. Of course, this is only if you want that cultural experience. Other than that, I would agree that if your focus is culture/Buddhism (Shinto too?) for the Kansai part of your trip to stay in Kyoto and take day trips to Nara, Osaka, and if you like castles, Himeji.

I'm interested in all forms of Buddism. in 2015 I visited India/Bhutan/Thailand ...

@all thanks for so much great advise. Will spend the next weekend investigate

If you can't get to the sumo tournament in person, it's easy to catch it on Japanese TV. Some stations do bilingual broadbcasts, so if you hit the right button on your remote, you can hear the commentary in English.

In fact, as a general rule, you cannot visit the sumo stables during tournaments. Seeing how the athletes live and train could be more interesting that seeing the actual tournament in a huge arena.

Don't rush Tokyo. There is something for everyone there and it is intriguing. Take note of the advice to concentrate on Kyoto. If you really want to see Osaka you can do it for a few dollars on a short commuter train ride on the spur of the moment. There is an excellent Limousine bus service from Kyoto Station to ITM, takes a bit under an hour and there are very frequent departures.
Have you checked out the airpass vouchers available to foreigners? Each voucher costs about Yen10,000 and is good for one sector, length immaterial. One sector from Kyoto to Okinawa is really great value. You could manage Okinawa to Sapporo on two vouchers! Astounding

Have not checked the airpass out but definitively will do so over the coming weeks (as plans solidify)
Osaka is off the list and I will spend more time in Kyoto with possible day trips

Hi,

After my European trip with my niece is over I have some time to think about Japan again. And I already changed it ....
You might do something like this:
Depart 3/22 and arrive 3/23 at 9pm in Haneda > just into a cab/car service to Yokohama
nights of 3/23-25: stay at the IC Yokohama (my wife always needs a day to sleep/recover from long flights so we won't do much on 03/24 so Yokohama IC was cheaper than the ANA IC Tokyo)
take the train 03/25 (7 day pass) to visit Kamakura / Hakone / Kyoto / Nara ..... not sure on how to do this best (how many nights where etc.)
03/31 - 04/02 (10am flight out of HND) in the Hyatt Regency Tokyo (just have enough points for a club room)

Any good ideas on how to do Yokohama - Kamakura - Hakone - Kyoto - Nara .... back to Tokyo best (how much time to schedule in etc.)?

Thanks for all the advise

If you're going to be commuting into Tokyo from Yokohama, then a JR Pass will work, as long as you stay on JR lines. (There are other train lines that are not JR, and the JR Pass will not work on the subways.)