§34 in relation to the development plan; Definition of the immediate surroundings

On the opposite side (in the development plan) . . .
How much does this aspect count in the assessment of integration?

Not at all! Doesn’t matter, is irrelevant.

How is the "immediate surroundings" defined in practice? Does a similar city villa 80 m away still count as comparison building?

There is "actually" no interpretation for the word "immediate." In §34 it means: next door.
I can be pedantic too, since I work at an authority.
The word "actually" is added because authorities may also deal more liberally with (old) regulations. At their own discretion, so to speak.

The direct neighbors have a distance of 10–14 m, but some other houses in the street (outside the development plan) also have only 3–4 m distance – but 100–200 m away.

The excerpt is actually too much for me to see lines or details. If your neighbor is at 12 meters, the 10th house further has 4 meters, it may be that the authority recognizes and supports an imaginary building boundary that narrows roughly toward the 10th house. Then you would have to be around 10, 11 or 12 meters apart. But as I said before: the excerpt is not enough for me because I cannot recognize anything that can be "read."

This means that new buildings regarding their size, shape, height, design and use must be such that they visually and functionally fit into the already existing development.

Wow, a bit too much of everything. Shape and design are not part of it.
Still:
“Within the continuously built-up parts of the locality, a project is permissible if it fits into the character of the immediate surroundings in terms of the type and extent of land use, building method and the plot area to be built upon, and the access is guaranteed. The requirements for healthy living and working conditions must be maintained; the local image must not be impaired.”
Type and extent, building method: residential and semi-detached houses, open construction method, no multi-family houses.
Plot area: ratio of the house’s footprint to the plot.
According to my knowledge here, the volume and roof shape play a minor role and may be different. I wouldn’t bet on it.
City villas and bungalows do not exist legally, 1.5 floors neither, and what the difference between bungalow and single-family house is supposed to be now is also questionable. Arguing is pointless because we know neither the street scene, the houses nor the quirks of the building authority.

Hello,

in another topic I have explained the criteria for the insertion in more detail:

on §34:

Type of structural use:
It is obviously a residential area (possibly mixed-use area) and you are building a residential house. Thus, the criterion is fulfilled.

Extent of structural use:
The new building must fit in terms of extent. It may therefore only take comparable dimensions to those that are typical of the immediate surroundings. The immediate surroundings are NOT only the adjacent buildings. Roughly, one can assume that everything in direct line of sight is relevant (e.g., buildings opposite the street). Relevant dimensions are those perceptible from the outside and thus obvious, such as length, width, and height of the building. For gable roofs, both the eaves height and the ridge height are relevant. This indirectly makes the number of floors also a measure of structural use.
Often forgotten in connection with the extent of structural use is the ratio between built-up area and free plot area. This is basically limited upwards and can be further restricted by the surroundings. Likewise, the position on the plot is part of the extent of structural use (e.g., in the case of obvious building lines). The roof shape is not part of the extent of structural use.

The local appearance must not be impaired:
Interpretation matter of the authority. Major deviations can be regulated with this but are usually not relevant in practice unless you are building a neon-colored building.

The buildings in the area covered by the development plan are characteristic of the surroundings and thus influence your project, even though your project does not necessarily have to comply with the specifications of the development plan.

Based on the aerial photo and your markings, I would assume that a building with two full floors should not be a problem. I do not see the building line; as long as an adequate distance to the street is maintained, the house probably does not have to be exactly in line with the two neighboring buildings.

Best regards

The excerpt is actually too much for me to recognize lines or details. If your neighbor is at 12 meters, the 10th house further on at 4 meters, it is possible that the authority recognizes and approves an imaginary building limit that tapers towards the 10th house. Then you should be about 10, 11, or 12 meters apart. But as I already said: the excerpt is not enough for me because I can't recognize anything that can be "read."

House number 111 (parcel 165) is our property. Parcel 164 belongs to the family with house number 115 (parcel 163), parcel 164 is only built on with a small GDR garden shed, just like our property currently is.

That already helps. It is noticeable that there is a lot of uniformity on the left side with regard to the front building boundary/line. I don’t have the inclination to research the development plan right now, but at least clear lines and alignments were observed.

If you are unlucky, the new buildings on the right side will be viewed similarly, so you have to adapt to the residential houses (without summer houses), that is the imaginary line of 109 and 115. but it doesn’t have to be.

Vielleicht könnt ihr mir bei einer Einschätzung helfen:

Is there a reason why you don’t ask a professional, meaning an architect?

Is there a reason why you are not asking a professional, that is an architect?

We are currently still waiting for answers from him.

If you are unlucky, the same will be seen on the right side with new buildings, so you would have to adapt to the residential houses (without cottages), meaning the imagined line of 109 and 115. But it does not have to be that way.

That we are not allowed to build on the street side opposite according to the development plan is okay. But to design the building envelope so tight (only direct neighbors) would be quite harsh. Our house would fit within the building envelope by measurements, but that would mean giving up a lot of usable garden, instead we would have a large unusable front garden. This, I will call it, strictness is hard for me to imagine. So much and so colorful (shapes, sizes, etc.) has been and is being built in the municipality.

But making the building envelope so narrow (only direct neighbors) would be quite harsh.

Well, so far it’s only a guess.

however, that would mean giving up a lot of usable garden,

Why? You can also use the garden in front, especially if it has such a nice sun orientation.

instead we would have a large unusable front yard.

But you can also nicely place the double garage instead of a boundary building. Or with boundary building, but detached from the house. Or you can allow yourself a bit more courtyard space, e.g. for visitors. Personally, I always like having several garden rooms, where you can, for example, create a kitchen garden in the front garden. Nothing is certainly unusable. The trend is also moving towards a second terrace facing the public area; just as people used to have a bench next to the front door for peeling potatoes, now they want to enjoy the sunset on the street that’s not built up and chat with neighbors.

So much and so varied (shapes, sizes, etc.) has been and is being built in the municipality.

Is that now an argument against your “monotonous” townhouse or for your “colorful” location on the plot?

You have 44 meters length with 20 meters width, right? For such a plot, I wouldn’t think of a townhouse that comes very close to the boundaries on the left and right.