Itinerary assistance

14/4/19
Arrival to Tokyo at late evening; settle down and have a great dinner and prepare for first solo trip.

15/4/19
Fuji - visiting Lake Kawaguchiko and Chureito Pagoda, for expected Sakura blooming from forecast, and explore around. Return back to Tokyo at evening.

16/4/19
Nikko
Early morning Shinkansen to visit Nikko - explore around.
Take Shinkansen/ trains whatsoever and overnight at Yamagata

17/4/19
Yamagata - visiting Yamadera and Dao
Overnight at Yamagata

18/4/19
Nyuto onsen - explore around the area and stay overnight at Nyuto Onsen.

19/4/19
[NEED HELP!]
At first I was planning to visit Kakunodate and the samurai district in Akita Prefecture, but the forecast of the coming Sakura will not bloom until maybe a few days later/ not the best time to visit it as its yet to full bloom.
Where else can I go if I'm not going to?
Plan to got back from Kakunodate to Tokyo at evening.

20/4/19
Hakone day trip from Tokyo

21/4/19
Tateyama Kurobe Alpine Day trip from Tokyo; earliest Shinkansen .
Return back to Tokyo at evening

22/4/19
Explore around Tokyo city until the late midnight plan back home.

I have been to Osaka, Kyoto, Fuji and Tokyo itself so wish not to stay long in the city. I am not a city person.
Is my itinerary very pack?
I need help after the Nyutou Onsen and where should I go?

:)

Very busy. Some routes use infrequent bus services. I think you'd struggle to do it.

Sakura forecast is a forecast. Reality will be somewhat different. Also the flowers bloom over many days. So you need to be somewhat flexible.
I would not skip Kakunodate. It�fs a nice place anyway even if you are too early/late for Sakura.

And yes as PP said, some of your days are too busy considering the transportation options you have.

Enjoy your trip to Japan!

There's no shinkansen to Nikko. You can take the shinkansen from Tokyo to Utsonomiya, but after that it's another +/- 45 minutes by 'regular' train.