Japan for three weeks in march

Hi,
I'm planning a trip to japan in march. The main focus of the trip will be Kyushu but im also spending some time with my friend in Osaka. I was hoping to get some opinions/suggestions on my itinerary from some more experienced travellers. I will be doing this trip solo

9/3 (friday) Australia to Osaka
10/03 (saturday) Nipponbashi (anime section), Mari kart. Maid Cafe lunch. Umeda Sky Building
11/03(sunday) Osaka musuem of housing/Farm house muesium? Night at USJ
12/03(monday) Day with friend. Baseball and Dotoburi(walk, gilco sign and ebisu bridge)
13/03 (tuesday) Day with friend. Shinsekai, Tsutenkaku and America Mura?
14/03 (wednesday) Sumo
15/3(Thursday) Osaka to Kyoto. Kifune temple and lunch at kibune. Gion at night. Night in kyoto
16/3(Friday) Fushimi Inari Shrine. Arashiyama. Night in Kyoto
17/3(Saturday) Osaka to Hiroshima. Hiroshima's Peace Memorial Park
18/03(sunday) Hiroshima to Fukuoka. Shofukuji Temple? Fukuoka Castle Remains. Dinner and walk
canal city ( Hakata Ramen). Night walk along Naka River
19/3(Monday) Fukuoka to beppu. Hells of beppu. Steam cooking. Pick up rental car. Night in yufin?
20/3(tuesday) Morning in Yufin. Yufin to Kurokawa. Night in Kurokawa
21/3 (wednesday) Kurokawa threw mount Aso to Takachiho Gorge. Drop car off in Kumamoto
22/3(Thursday) Day in Kumamoto. Kumamoto castle,Sakuranobaba Johsaien &Hosokawa Mansion.
Try horse meat. Suizenji Garden after lunch
23/3(Friday) Kumamoto to kagoshima. Ibusuki Onsen Shiroyama lookout.Night in kagoshima
24/3(Saturday) Jet foil to Yakushima. Night in Yakushima
25/3 (Sunday) Yakushima
25/3 (Monday) Yakushima to Kagoshima. Kagoshima to Nagasaki
26/3 (Tuesday) Day in Nagasaki
27/3 (Wednesday) Gunkanjima
28/3 (Thursday) ?
29/3 (Friday) ?
31/3 (Saturday) ?
1/4 (Sunday) Osaka to Australia

All exploring around the cities will be done via foot and public transport. Osaka to Kyoto will also be done via local train (about 500 ‰~, 1/2hr).

Osaka to Hiroshima, Hiroshima to Fukuoka, Fukuoka to Beppu, Kumamoto to Kagoshima and Kagoshima to Nagasaki via Shinkansen. Expensive but all seemed a relatively short travel time. I checked on hyperpedia and it seemed ok to leave around 10am on each transfer. That gives me time to grab breakfast and not have to run for the train.

Beppu threw to kumamoto via rental car so i can see Mount Aso and Takachiho Gorge. Its meant to be a nice drive

Kagoshima to Yakushima via jetfoil or ferry maybe. depends on what i can book tickets for in advance

If i need to free up time im not fussed with Fukuoka as there didn't seem to be a heck of a lot to do (just a city).
Dont think i should write off a day just for Gunkanjima as it should take about three hours, depending if i can even go. But wasn't sure whether id be pushing myself to merge with the day in Nagasaki on the 23rd
Also not sure what to do with the last three days

19/3(Monday) Fukuoka to beppu. Hells of beppu. Steam cooking. Pick up rental car. Night in yufin?
20/3(tuesday) Morning in Yufin. Yufin to Kurokawa. Night in Kurokawa
21/3 (wednesday) Kurokawa threw mount Aso to Takachiho Gorge. Drop car off in Kumamoto

These days are too fast. With you spare 3 days. I'd add one for Yufuin overnight. So Beppu, Yufuin and Kurokawa overnight. Just adding one day will free up this for the following to days.

If it is your first time to Kyoto and Fukuoka, I'd add another day to both those cities also, as you don't really have enough time.

Thought about visiting Miyajima near Hiroshima?

Thanks for the suggestions about Beppu, Yufuin and Kurokawa. I did kinda want to spend sometime just relaxing soaking in the sceneary

I've been to Kyoto before so this time was just to see a few things i missed last time.
Im not too sure what else there is to do in fukuoka though? any suggestions? as it just seemed like a city

I did look at miyajima but i didnt think id have the time to visit