Itinerary for three weeks in Japan

Hi,
We are a couple planning a three week trip in Japan. We could use some advice with planning our trip. Our plan is to mostly use highway buses as they are cheaper and we are traveling on low budget.

This is the plan we came up with so far:
18.4 - evening, landing in Fukouka.
19.4 - spending half a day in Fukouka and taking a bus to Kagoshima. Spending the night in Kagoshima.
20.4 - spending the day and night in Kagoshima and around.
21.4 - 22.4 - bus to Kumamoto, maybe trip to mount Aso
23.4- bus to Yufuin, spend the night there.
24.4 - bus to Hiroshima, spend the night there
25.4 - spend the day in Hiroshima and Miyajima Island
26.4 - bus to Okayama, ferry to Teshima. Spend the night?
27.4 - ferry to Neoshima
28.4 - bus from Okayama to Kyoto
29.4-2.5 - Kyoto, side trip to Nara
3.5 - bus to Takayma, spend the day there
4.5 - bus to kamikochi and back to Takayama, night bus to Tokyo
5.5-10.5 - Tokyo.

We would love to receive any advice or tips regarding our plan.

Thank you!

interesting route. i like it. sorry that i dont have anmy other feedback, but i think it is pretty nice.