When you research Kyushu please look at southern half of Kyushu also. Miyazaki, Kagoshima, and Ibusuki are not that bad of area, either.

If you want to go little further then Kyushu has islands you can explore: Tsushima island located between mainland Kyushu and South Korea, Goto islands western shore of Nagasaki.

Also do not forget islands south of Kagoshima are also part of Kyushu. Tanega island where rocket launch take place, home of Japanese space exploration. Yaku island which is registered as Natural World Heritage site by UNESCO. Amami-Oo island is the biggest of southern islands of Kyushu and popular tropical tourist destination. Tokuno island is smaller island south of Amami-Oo island, tropical island closer to Okinawa but still part of Kyushu.

If money is not an issue then as a train geek I recommend train Seven Stars by JR Kyushu to tour around mainland Kyushu. JR Kyushu also happened to have a lot of fun tourist trains around Kyushu which is economical.