How can I make my itinerary less rushed?

Hey there, I am Tom from Germany. Just checked Patrick's itinerary (other Thread by star78) and now I am pretty unsure about my own again.
We will arrive on 21th August 15:00 and need to return the car on 30th August by 15:00

So far my itinerary was as follows. Except ferries we want to avoid toll roads completely.

21th: arriving in Fukuoka; maybe a few ours to check out the city
22th: To Sasebo along the coast. On the way, make a stop in Karatsu. Spend the rest of the day in and arount Sasebo
23th: From Sasebo to Nagasaki. Stop in Arita
24th: Stay in Nagasaki
25th: Nagasaki – Unzen/Shimabara – Shimoshima – Kagoshima (this section is probably insane ;)
26th. Sakurajima walking/hiking – udo jingu – stay for the night somwhere arount Aya
27th: Suspension Bridge – Takachiho (Gorge) – Stay somwhere in/around Takachiho
28th: Takachiho – through Aso – staying somwhere around Kuju san
29th: Stay around Kuju san. Maybe hiking, checking out Onsen, Yufuin
30th: Back to Fukuoka and return car – stop by Nanzoin temple

31th: Continue towards Kyoto and later Tokyo but this part is not 100% clear yet.

Now that I read Patricks reprot, I wanna go to Kunisaki as well.

I generally have the feeling that it is extremely rushed. Never staying somewhere for more than 1 night except Nagasaki. I remember our trip to the eastern part of USA last year. We often stayed for 2 nights, in Washington DC even 3 nights but even that seemed rushed ;)

Don't know what to do. I know I will come back to Japan many more times anyways. Still, should I skip Sasebo and head directly to Nagasaki making a stop in Karatsu&Arita. And should I cancel Shimoshima and Sakurajima/Kagoshima, too and go from Nagasaki to Kumamoto instead and focus completely on the northern part of Kyushu? Kyushu is just half the size of Bavaria where I am from, still it seems way too big to explore in on trip.

In the beginning I even considered Yakushima but dropped that idea pretty quickly ;)

I've tried at "Google.de".
https://goo.gl/maps/ZCoQCwBagrq

The average speed during the day time is arond 40km/h including signal stops and short breaks.
Fuel consumption depends on the type/name of car, so please check it.
The gasoline(fuel) fee is currently close to 140Y/L(regular), but do not know how the price in August is.

You can learn about traffic rules and how to use gas stations are written in this PDF.
http://www.hkd.mlit.go.jp/topics/toukei/chousa/h20keikaku/e/e_all.pdf

If unfortunately a large typhoon landed, it may be impossible to move 2 or 3 days.
https://youtu.be/nhY0_6VF9Ag
https://youtu.be/vPAfEh4S5zE
You'd better not pack too much, also will be really hard even if continue super hot days(over 35��).
https://weathernews.jp/s/topics/201707/300045/

Without meaning to sound rude. You will be spending most of your time driving. Have you considered using the trains? If you really want to drive then I would still suggest a similar itinerary. If you don't have the car booked then you could use the trains for the Sasebo & Nagasaki sections & hire a car in Nagasaki to drop off in Fukuoka

I would probably drop Karatsu unless you really have something in particular you want to see & go from 22nd Fukuoka to Sasebo possibly on to Nagasaki in evening (2 hours train Fukuoka to Sasebo).
23rd Sasebo to Nagasaki and Nagasaki sightseeing
24th Nagasaki
25th Nagasaki to Kagoshima. (Make absolutely sure of the ferry times)
26th Sakurajima etc
27th Kagoshima & area (Lots to do round here)
28th Northwards Takachiho gorge & stay near Kuju.
29th Kuju Hiking? Yufuin?
30th Fukuoka

This is just me freewheeling. I use the trains so I don't know if these driving times are reasonable. I don't know where you will be staying in Nagasaki but I wouldnt want to drive near Nagasaki station. That junction is nuts. I would miss Mount Aso as I'm not sure if it's open again. This plan does give a couple of three night stays in a city to allow for bad weather, plan changes etc.

If I have anything badly wrong I'm sure others will correct me :)