Hello, Kai, and thanks a lot for your post. I quite agree with you that one should never accept a position that does not provide Z visa issuance and contract in advance.

Do you mind telling us the name of the school/organization?

Also, these types of prep-for-study-abroad ("international") programs are also full of traps (I know from experience). I strongly suggest that FTs steer clear of these types of jobs.

Have you worked in such programs before?