Thank you for your advices!
The main fault I did was to use too much overlapping. On one side it's logic: more pics to stich, more 'errors' possible. I was going with the idea, that more info/pics used, better the matchings can be done by ICE. In fact, more than 40% overlapping is useless and contraproductive here.
As I do no money with my pano's (and other pics), the Photoshop is far too expensive for me.