If I didn't know that You and He mean this seriously, then it would be both funny and sad at the same time. After seeing the numbers, I can only say that He would have sent you into personal bankruptcy without batting an eye. For the house, you would have been short at least €150-200k. Morally bottom of the barrel. Good that you registered here.
But since I have been talking myself hoarse until now and you still talk about individual trade contracts and engineer, it really gets too stupid for me. Listen to the people here who have experience and cut off all contact with the engineer. Have a house built by a general contractor.