Kyushu Travel: Kagoshima and Fukuoka

I am interested in spending a 4-5 day leg of a trip to Japan in Kyushu, and I'm looking at splitting that between Kagoshima and Fukuoka. Interested in all kinds of things: food, nature, history. I'm sure I can find things in both but I wanted to ask is that too jam packed? Ideally I'd rather just pick one spot and really get to know it, but didn't want to pass up the chance to see Kagoshima while so close. Thanks!