Japan Rail Pass does not sound best.
Takayama, Shirakawa-go and Kanazawa are connected by bus;
you don't have to rent a car or drive by yourself.
https://www.japan-guide.com/bus/shirakawago.htmlH:
Redo the itinerary so you don't backtrack twice.I agree.
I suggest you change the order of the places,
to save your time and cost.
When you don't turn back the way,
the JR regular cost for Days 2 to 8
(until you get to Tokyo)
is estimated as up to 22970 yen,
which is lower than the price of 7-day Ordinary-class JRP,
by several thousand yen.
JRP can cover your trip from Tokyo to Odawara and back.
On the condition that you use Hakone Freepass
and pay additionally the surcharge for Odakyu Romancecar rides,
the cost of your round trip from Shinjuku to Odawara
is calculated as 3100 yen (#1).
https://www.japan-guide.com/e/e2358_008.htmlIf you choose JR Tokaido Shinkansen over Odakyu Romancecar,
JRP is still worth considering;
otherwise, JR regular tickets seem more suitable.
(#1) The gap of the prices between
Hakone Freepass for the free usage area only
and
Hakone Freepass covering Shinjuku to Odawara round-trip basic fare
is 1100 yen;
the Romancecar surcharge is 1000 yen per way for this section.
----
Kyoto -- Gero -- Takayama (#2, #3) by JR within 3 days
: 4840 yen as basic fare.
Kyoto -- Gero on Limited Express Hida (#2, #3)
: 2750 to 3350 yen as Limited Express surcharge
for your ride with your seat reserved.
Kanazawa -- Tokyo by JR within 4 days
: 7480 as basic fare.
Kanazawa -- Tokyo on Shinkansen Kagayaki
: 6700 to 7300yen as Shinkansen surcharge
for your ride with your seat reserved.
((JR regular cost: 21770 to 22970 yen.))
Takayama -- Shirakawa-go by non-JR bus
: 2600 yen.
Shirakawa-go -- Kanazawa by non-JR bus
: 2000 yen.
Hakone Freepass (2-day)
covering Shinjuku to Odawara round-trip basic fare
: 6100 yen.
Shinjuku -- Odawara on Odakyu Romancecar
: 1000 yen as Limited Express surcharge.
Odawara -- Shinjuku on Odakyu Romancecar
: 1000 yen as Limited Express surcharge.
(#2) There is one Limited Express train
running daily from Osaka via Kyoto, Gifu and Gero to Takayama.
Limited Express Hida 25:
Kyoto (08:31 or 08:34, Track 0) -- (11:29) Gero;
Track 0 platform is near Central Gate.
(#3) Between Gero and Takayama,
trains are only very infrequently available,
and Limited Express trains do not go notably faster than Local trains.
Departure time of some Takayama - bound Local trains from Gero:
20:49 and 22:26 in the night,
07:35, 07:52 and 09:00 in the early morning.
----
With one or a few destinations
such as Gokayama and Kurobe Gorge,
Takayama-Hokuriku Area Tourist Pass
may work well and save your cost.
This tourist pass can cover the bus fares,
but cannot be used for Kyoto -- Gero -- Takayama direct route.
https://touristpass.jp/ja/takayama_hokuriku/