Development plan and the resulting house plan

Gable roof with 22 to 28° pitch and vacuum cleaner knee wall (as well as the small delta between the floor area ratio and the plot ratio) I read as a clear statement that only two house models are desired here: namely the literally understood "one-and-a-half-story" with an attic sitting at the kiddie table on a ground floor that wears the pants; or the bungalow with a storage attic.

I think that calls for a bungalow. 130sqm fits well there.

“A full storey is a above-ground storey that has a clear height of 2.20 m or more over at least half of its floor area. A top storey is only a full storey if it has the clear height mentioned in sentence 1 over more than two thirds of the floor area of the storey below.”

This applies in Lower Saxony. For Bavaria, the following applies:
Art. 83 BayBO currently
(6) As far as § 20 para. 1 of the Federal Land Utilization Ordinance refers to state law for the definition of a full storey, Art. 2 para. 5 in the version valid until December 31, 2007, shall continue to apply in this respect.
Art. 2 para. 5 BayBO 1998:
Full storeys are storeys that lie completely above the natural or designated ground level and have a height of at least 2.30 m over at least two thirds of their floor area.
The Bavarian Chamber of Architects explains:
By height, the height measured from the top edge of the floor to the top edge of the floor or to the outer roof covering is meant, not the clear room height.
But anyway, with DN28 and no dormers, it will not be a full storey anyway.

I just don't understand the severe restrictions in the development plan.

Then have the justification for the development plan given to you today. It should explain why it was set so restrictively. If it takes so long (2001-2020) until the development plan can be implemented, there were and presumably still are considerable objections from various interest groups.

So the development plan has been established since 2001. That all fits well. The "problem" with my rear property was that this street has been planned since 2001. But the city was missing one plot. Namely that of our neighbor. Until 4 years ago, an old lady lived there who did not want to sell her property. Thus, a part of the city was missing and they could not build the street. The lady passed away 4 years ago. There was a community of heirs who had disputes. One of them initiated the forced auction. Thus, he acquired everything himself. But a company had a right of first refusal on parts of it, which it exercised, and the city also exercised the right of first refusal on the missing property for the street and secured it. According to a telephone statement, the street will now be built in 2020. But I will try to go to the municipality later.

Thank you for the correction. But in the end, it has no effect due to the roof pitch and the low knee wall.

I would build a bungalow with the apartment for you on the ground floor and under the roof (maximum pitch) then accommodate the study and storage/possibly technical equipment. I think you can get a nice house there.