Your itinerary already has various sites to visit,
but still I suggest Matsumoto and Yoshino,
on the condition that you extend the itinerary by one day.
Cherry blossoms, on the average,
are best seen from early-to-mid - April at these two places.
- Matsumoto
https://www.japan-guide.com/e/e6050.html- Yoshino
https://www.japan-guide.com/e/e4150.htmlAlso, I would shift Takayama to around April the 14th.
The spring Takayama Festival [Takayama Matsuri]
is held on April the 14th and the 15th.
- Takayama Festival
https://www.japan-guide.com/e/e5909.htmlMy idea for your itinerary
(after a few days in Tokyo) is shown below.
Here I choose Tsu instead of Nagoya as a gateway to Suzuka,
add Matsumoto, Yoshino and Kobe,
and skip Shirakawa-go,
which sounds better during winter to visit.
Tsu City is Mie Prefecture's capital.
JR-Central, Kintetsu Railway and Ise Tetsudo
each have Tsu Station, sharing the same venue.
Kobe is known well for many things,
and the night view is one of them.
- Kobe
https://www.japan-guide.com/e/e2159.html----
Idea for your itinerary:
Apr. 1 (Monday)
: Matsumoto.
: Kanazawa in the evening.
Apr. 2 (Tuesday)
: Kanazawa.
: Kyoto in the evening.
Apr. 3 (Wednesday)
: Kyoto.
Apr. 4 (Thursday)
: Yoshino.
: Tsu in the evening.
Apr. 5 (Friday),
Apr. 6 (Saturday),
Apr. 7 (Sunday)
: Suzuka F1.
: Tsu in the evening.
Apr. 8 (Monday)
: Nara.
: Osaka in the evening.
Note:
Kintetsu Rail Pass (5-day) can be used
for Kyoto -- Yoshino,
Yoshino -- Tsu,
Tsu -- Kintestu-Nara
and Kintestu-Nara -- Osaka-Namba;
you pay additionally the surcharge for Limited Express.
https://www.japan-guide.com/e/e2357_006.htmlApr. 9 (Tuesday)
: Koyasan.
: Osaka in the evening.
Apr. 10 (Wednesday)
: Himeji until around noon.
: Kobe until the early night.
: Kyoto in the night.
Apr. 11 (Thursday)
: Kyoto.
Apr. 12 (Friday)
: Kyoto.
Apr. 13 (Saturday)
: Takayama.
Apr. 14 (Sunday)
: Spring Takayama Festival - Day 1.
: Kyoto in the evening.
Apr. 15 (Monday)
: Hakone.
: Tokyo in the night.
Apr. 16 (Tuesday)
: Tokyo.
Apr. 17 (Wednesday)
: NRT.