Floor plan - house planning carried out by a civil engineer

oh yes, and our children's rooms on the upper floor can later be converted so that they can access the attic from the rooms, for example to [Schafgalerin]... These will then be wonderfully large children's rooms in which two children can live together comfortably.

Where did the OP write that? He basically wants three children's rooms, a study, a double garage (in my opinion all legitimate). He wants to spend 310,000 euros on that. That could be the stumbling block.

He didn't write it, but that's what the current room plan looks like. Basically, the goal is achievable; we are currently building with 4 children's rooms (3x18m², 1x12m²) with a total of 175m² living space and are just under 300k€, purely for the house including the basement. One of the children's rooms is in the living basement with its own terrace and its own bathroom.