I always prepared a second and a third alternative with other schools that
had offered me a suitable position

It's my understanding that it's illegal to work directly for a school, that's how it was explained to me by the helpful police officer: as a FT (on both the study and the working visa) you must always operate through a third party, and they must pass it through the local government operator, E.g. FT -> Contractor -> Local Gov't -> School.

you have to calculate additional
expenses for hotels and inland travel by train or plane to get to the othern place.

This simply wasn't true for anyone on our intake- Enfly kindly provided me with hotel accomodation during the training week, and also for three days whilst my apartment was being prepared/cleaned ready for me to move in. This makes me question whether you're actually on the same page as the rest of us?

acting like an adult also includes
staying clear of schools that lie to you and that you should therefore not work for.

This is more a case of integrity rather than maturity. Personally I've experienced nothing but positives with my school; yes, the (dis)organisation over here takes getting used to, but just chill and roll with it, make sure to ask your contact teacher and anyone watching your lessons for feedback and advice, and even sound out the students to see what they think.