14 days Nagoya, Kyushu and Osaka

I am planning 14d trip in early April, I hope to fly in to Nagoya and fly out from Osaka.
Mainly sight seeing, not too pack. Would like to visit Tateyama, Achi for star gazing, hoping if time permitted can go to Kyushu area, if not, then Osaka for sightseeing and shopping.
Should I drive in Nagoya and then train to Osaka?
What is best way?
Thank you

Can you clarify the places you want to visit:
Achi in Nagano prefecture? Which place specifically? This seems a very remote, mountainous region, so a car is probably called for.
Tateyama in Toyama prefecture? Or some otger mountain called Tateyama? If Tateyama in Toyama prefecture where specifically? The Tateyama Kurobe Alpine route?
If that, its quite far from Nagoya. You�fd probably go from Nagoya to Toyama by train and the from there all the way by public transport through the Alps and in tge other end you finish in Nagano prefecture. But far from Achi.

14 days you can easily do all that. Get a 14 day rail pass.

4 days Nagoya, do whatever you have planned.
Travel to Kyushu using shinkansen.
4 days there to do northern touisty stuff, Fukuoka, Nagasaki, Beppu, Yufuin etc.
Travel to Osaka using shinkansen.
4 days in Osaka, do whatever you have planned.

Thanks for replying.
Tateyama is the Tateyama Kurobe Alpine route and Achi is Achi-mura in Nagano ken.
I think I will skip kyushu for this time as don't want to rush through.
Should I fly in from Tokyo or Nagoya and fly out from Osaka?
Thank you 😊