According to the floor area ratio, only 138 m² is possible - 2 floors - Help :)

First of all, a plot ratio of 0.15 is a real luxury. Since this also applies to the neighbors, it guarantees privacy, a house with distance to the next one, lots of green. Thus, the complete opposite of the 0.4 plot ratio urban villa deserts in white gray with boxwood in granite gravel beds in front and Q5 on the clinical driveway.
With the size of the plot, a 10 by 13 house plus terrace is feasible, 10 by 13! That means, with an upper floor, easily 145 sqm of living space. Well, if that’s not enough for someone. I see zero problem with the planning. Karsten

No honey, not plot ratio... here the 0.15 applies to the floor area ratio!

Oh, my angel. Well, it's quite loosely built there. There are pictures now.

Once again - trees in front of Osten go away

No honey, not floor area ratio... here it is 0.15 on the floor space index!

It hasn't been really clear so far ;)

The neighbors to the north surely exceed both. I also suspect three more properties. Therefore, I would give a good chance of an exemption.

Which ones are meant?

The entrance is from the east

It's exactly like the development plan is a matter of interpretation. I say the entrance is from the north. Well, you have to walk up the entrance stairs from east to west. But you enter the house from the north. The red arrow in #77 is definitely wrong.

It hasn't been really clear so far

Since I don't really consider the mentioned contradiction in the development plan enforceable (whether legally or pragmatically I leave open) and I don't know the texts of the development plan, I assume that the floor area ratio is actually 0.15.

Which ones are meant?

138/7 and 138/8 as well as 139/3, 141/2 and 138/9 (apparent estimate)