National Pass vs Regional Pass/single tickets

Hi!

We're staying in Japan for 21 days in octobre, travelling from Chubu Airport to the south (Fukuoka) and back, with longer stays in Osaka/Kyoto, Hiroshima/Nagasaki. (Timetable not yet fixed, but about Nagoya-Osaka day 1, Osaka-Fukuoka day 8, Fukuoka-Nagasaki day 13, Nagasaki-Nagoya day 17 or so...) We will probably go for lots of day trips, but rather short ones (like visiting Uji and Nara from our Osaka base, Beppu from Fukuoka or Ise from Nagoya), so not that regular use of Shinkansen or other fast trains. From what I checked by now, I figure it will be cheaper for us to buy single tickets and maybe a Kansai regional pass for the time of our stay in Osaka than buying a JR National Pass. Would you agree?

Thanks for your advice!