Takachiho to Aso via Takamori

Hi

I am planning to spend a night in Takachiho. I will take a bus from Kumamoto in the morning and arrive in Takachiho at midday.
The following morning I am hoping to be able to get an early morning bus from Takachiho to Takamori and then take the 852 train to Tateno and then to Aso arriving at 1007. I want to then visit the caldera, before taking an afternoon bus to Kurokawa onsen.

Firstly, is this a viable plan? Is there a bus that leaves Takachiho for Takamori that early? There doesn't seem to be any other way to get to Mt Aso.

Secondly, is this plan too rushed for Mt Aso or should I spend the night in Mt Aso and then head for Kurokawa onsen the following day?

Thanks in advance!

Firstly, is this a viable plan?

It seems to me that the number of buses between Aso and Takachiho has been reduced to two per day:
http://www.kyusanko.co.jp/sankobus/toshikan/takachiho/20100801/takachi...

高千穂バスセンター is Takachiho Bus Center
高森中央 is Takamori Chuo near Takamori Station
阿蘇くまもと空港 is Kumamoto Airport
熊本交通センター is Kumamoto Kotsu Center in the city center
熊本駅前 is Kumamoto Station

This means that you will have to take take morning bus, which leaves Kumamoto around 9am in order to arrive in Takachiho at noon. This will not be a lot of time in Takachiho, but it might be possible to see most sights, some of which require an additional local bus ride to be accessed.

On the next morning, it is impossible to be in Takamori by 8:52. But that does not mean that seeing Aso and then continuing to Kurokawa is not feasible. You will have to further check bus and train schedules, as the trip from Takachiho to Mount Aso requires multiple transfers along the way.

If anyhow possible, I strongly recommend to do this trip by rental car. With a rental car you would have almost twice as much time for actual sightseeing. It would be much faster for getting to and around Takachiho and for seeing Mount Aso:
http://www.japan-guide.com/e/e2024.html

This is what I posted for someone in TA recently with updates for your case.
There are three ways to go to Mt. Aso　from Takachiho. The bus leaves 8:31 at Takachiho.
1. There are direct buses from Takamori Chuo only on weekends & holiday.
2. Get off at Takamori Chuo(arr. 9:39) and take a scenic Minami Aso train to Tateno, dept. 9:45 (Torokko sightseeing train (470yen+500yen) on weekends+holidays Mar.1- Nov. 30) arr. 10:32 or a reg. train dept.10:28, arr.10:54(470yen).
2.1 Then, take either connecting JR train to Aso station & a bus to Asosan-Nishi ropeway station
2.2 Or the Cross Kyushu bus(Aso 1-Go from Tateno(dept.11:20) to Asosan-Nishi rope way stationi(1,120yen). See Aso 1-Go below.
3. Another is to get off at Kumamoto/Aso airport(arr.10:28) and catch a Cross Kyushu bus coming from Kumamoto to Asosan Nishi Ropeway station(Aso 1-Go dept.10:50, Arr. 12:06, 1,490yen).
This Aso 1-Go has 90 min. lunch & volcano sightseeing break from 12:06-13:36. The fare from Kumamoto AP to Kurokawa onsen is 3,850yen including lunch(1,050yen) but the cable car ride is extra. The fare is higher due to additional RT legs from JR Aso to Asosan Nishi station+lunch box.
If you get off (w/o lunch) here & take the later Kujyu 5-Go bus from JR Aso dept. 16:26, Kurokawa onsen arr.is 17:14 & 960yen
Aso volcano sightseeing info.
http://www.kyusanko.co.jp/aso/english.html

Thanks so much to both of your for your answers. This has helped a lot!