Floor plan design single-family house approx. 250 sqm with granny flat

Regarding privacy: this can be achieved through the design of the garden when it comes to shielding from the street.
Regarding the location of the living room: surely, it is rather unusual not to design it with lots of light and an open view outside, but it is a conscious decision to make this area somewhat "cavelike." I lived for a few months in an adobe house in New Mexico. The "dark" living room worked very well there – although the lighting conditions and climatic circumstances are incomparable to anything we have in Central Europe. It’s not my preference – but that doesn’t mean anything.
Have fun with the fireplace builder. Be open and don’t pre-judge the result through your questions.

Thanks, that is roughly the idea behind it. I have a nice view of the garden from the dining area; in the sofa area, I deliberately don’t want huge glass surfaces and find it cozier when it’s more enclosed. Not everyone has to like that, but it’s not such an exotic layout as claimed here and, by the way, copied from a very expensive architect-designed house that we really like. So apparently a professional also once considered it acceptable.

We will enlarge the dining area a bit more (I’m writing this at least for the third time). I don’t understand why a passage past the dining table must always be problematic, as long as there is enough space, which can still be optimized. Even with the current construction, with the fireplace between the sofas, the windows to the right and left of it could be floor-to-ceiling, and one of them could be designed as a door to the terrace, providing a second access.

Privacy in the south and west towards the street we would like to create by planting a beech hedge [Rotbuchenhecke] along the property boundary and, of course, through additional planting closer to the house / on the terrace.

Regarding privacy
Have fun with the stove builder. Be open and don’t anticipate the result through your questions.

We will be. This morning we had the discussion that we maybe don’t trust the banana republic Germany, which despite record tax revenues no longer reliably manages the core tasks of the state, with its completely botched energy transition, to provide consistently enough electricity to operate the heat pump, and therefore the idea of a stove as a backup should be discussed again, which of course would open a much bigger can of worms. We will think about this in the next few days and possibly use the appointment with the stove builder to discuss the options available there.

and therefore the idea of discussing the stove as a backup once again would be,

An important aspect for us regarding wood stoves as heating was the health benefit provided by the radiant heat. This is not relevant for everyone. However, anyone who has had to deal with the topic of depression and has experienced a connection with the winter season will not deny this. We heat our living space (we have three separate "one-room" apartments in our wooden cabin) exclusively with wood. Due to the combination of electronic combustion control and heat storage mass, one load of wood is sufficient every 24 hours even at single-digit minus temperatures. The picture shows the fire at startup.

It's too exhausting for me to argue against your entrenched beliefs. If you absolutely want to block access to the terrace, then go ahead. Maybe you should go ahead and install the lintels in advance. If someday the penny drops that you practically never turn on the fireplace in a new building because it's too warm and you would much more likely need the garden access at that spot, then at least you can still remove that thing again.

not enough trust to consistently provide enough power to operate the heat pump and therefore the idea of the stove as a back-up would be worth discussing again,

Just remember the week-long power outages of the last 10 years and the discussion quickly ends with the conclusion "the stove is great for the look and the feeling, but I don’t need it as a heating replacement."