Rough construction plan draft for a single-family house including double garage and entrance

Have you already calculated the built-up area?
The existing garden house will also have to be included. I don't know how it is in Bavaria, but over 30 sqm equals over 50 cubic meters, ... I don’t know for sure though, it's rather derived knowledge ;)

But the house is too long. Does the 3-meter boundary construction also apply in Bavaria?
Then there is the height, I lack the knowledge of how that is calculated.

The staircase must of course be within the building window. Also think about a parking space for the granny flat and make sure that the technology is built within the thermal zone and not outside. Whether that makes sense as you imagine it, I don’t know.

Whether it makes sense the way you imagine it, I don't know.

From my point of view, we are still half a dozen drafts away from the final version. The stage "practiced in the drawing program" has been reached, but the sense for dimensions is still in its infancy, and they probably haven't really been checked against the requirements yet. For example these points

The garden shed on the property will also have to be taken into account. [...] Then also think about a parking space for the granny flat

I see the same.

The floor area ratio is 1.1

Why? According to 2.1.2 it is 0.8. But with 636m² plot area it doesn't matter anyway.

This is to be divided later into 636sqm and 1154sqm.

When later? After the building permit is granted?

Can I currently use the 1790sqm as the basis for calculation or do I have to assume the later divided plot?

If the building application is submitted for the entire plot, you assume 1790m². Then the existing building stock must also be calculated.

What do you mean it does not fit into the building envelope?

You have to stay within the blue lines with your floor plan. But it looks like it does not fit geometrically. Therefore my urgent recommendation is to print out the (future) building plot to scale and precisely map the building boundaries (blue lines) into it.

We have such a shortage of living space that almost everything is approved nowadays.

Knee wall, eaves height? Is the community indifferent to everything as well? Then the community should repeal the development plan.
A reduction of the 3m minimum distance will certainly not be approved, unless your neighbor agrees.