Aso san will not take the whole day. A friend drove to the top may be in one hour from downtown. Due to gases, you cannot stay too long at the top anyway.

There should be a flight from Kumamoto to Haneda, may be two hours duration. The airport bus from downtown is very convenient and may be about Y500.

Kanazawa is worthwhile and late Oct is usually start of crab season. Try to find a flight as jib71 suggested.

Kanazawa central market

Added: There is a PM flight from Sendai to Komatsu on ANA. A little bit more than a standalone JR ticket. By train would be about 6 hours via Tokyo, Maibara. Likewise, there is a Komatsu to Fukuoka ANA flight. But I think picking up an egi-ben, a bottle of sake, enjoying scenery and talking with fellow travelers on a train is quite enjoyable.