Deviation from the development plan in the new construction area is possible

I'm going around in circles.

So, once again:
You want to build 5m from the northern boundary. Your setback requirement according to the state building code is 7.8m.
1. According to Art. 63, there is theoretically the possibility that the district office allows a deviation. However, it will not do so because your property can be reasonably and feasibly developed even without a deviation, and therefore the conditions for granting a deviation are not met.
2. The municipality changes the development plan so that it allows a setback calculation deviating from the state building code. Just as you yourself have written, in the sense of: For the properties north of the main access road, a setback of 5m (or 3m or 0.5H or 0.4H) to the northern boundary is sufficient.
3. You ask the neighbors whether they agree to accept the excess setback area on their property until the development plan amendment comes into effect. Then, in my opinion, no deviation requiring approval exists, and your exemption procedure can start.

...

... could... . A strip of 3m from the northern and southern boundary must not be built on, otherwise free choice of building position.

which in our case is not allowed, therefore unfortunately no free choice of building position.

I will ask the neighbors, but I see little prospects....for him it is very risky....if I don't remove it again at some point, his property remains encumbered.....but I will ask him.

Question 1) If you want to build so far back and downhill, how do you get rid of wastewater? 2) What is the purpose of the giant front yard? 3) Suggestion: Move the house as far as possible to the southeast. So that a lot of west sun can reach the land. Karsten

...for him that is very risky...

The risk would only lie in the fact that the amendment to the development plan does not become legally binding. You can already pay him the fees for the reversal in advance. Then he will no longer be dependent on you.

You ask the neighbors if they will take over the excess setback area on their property until the amendment to the development plan comes into effect.

Where/how is this takeover recorded if there is no servitude known in BY?