If you want to realize your dream within the budget, developing patience and calm will HAVE to become one of your new virtues.
You are now on the right track.....use the next few weeks for extensive inquiries and conversations with the architect who is friends with you and the building authority. Count on about 2.5 years + x for the matter. You need to clearly and demonstrably plan the construction project realistically. Especially for the bank.
YOU have to put energy into it now. You have to do something. And a lot.
ONLY YOU.
This phase then decides the feasibility and especially the ability to finance.
Since the new approach definitely fits the budget, you can become the captain now........
(and if it works out: I will keep the promise with the sausages in Berlin, I'll get on the plane and come over, sure).