Floor plan design single-family house solid wood construction 140 sqm in Lower Saxony

the employees there also have nothing to gain if they intentionally advise us incorrectly

It’s not about intentional incorrect advice. As in life, there are several ways to carry out something when building a house. As a company, one usually chooses the option that is good enough for the customer to accept and easiest to implement. This is not necessarily wrong, since customers tend to look at the price, and whoever offers the expensive option will be undercut by the competition ;)
When building, there is also the possibility to shift efforts to later trades. With an all-inclusive general contractor, all this remains their responsibility; with a shell house, the effort then ends up with the builder. That’s why you need someone who is knowledgeable and can advise you on what would be the best solution for you. And this is independent of the “we have always done it this way” problem, which often turns out to be no longer the state of the art for 10 years now.

Don’t get me wrong here. I think the project is great, and if you have a passion for it, all the better. But after various incidents with our construction, I would never again rely on someone who has a conflict of interest, but only on someone who is paid exclusively to represent my interests.

Do you perhaps have a rough "minimum dimension" for the HAR in mind based on your years of experience? Or are there DIN standards that must be met?

No, but I have had the problem myself. The recipient from the municipality complained because he could not install the meter. No matter how big the HAR is: a heating system is not placed tightly against the wall unless it is installed there. Installation and maintenance usually become clear afterwards with common sense. There is a DIN standard for the electrical box.

If the heater is placed too close to the wall, it will not be accepted.
A clearance distance _must_ be planned in front of the electrical box…

That too would be a significant point and, in the proposed floor plan, an argument to reconsider the mini utility room separated from the laundry room: because just imagine, with the next heater in twenty years being 3 cm larger, the working space for the technician at the adjacent electrical distribution would no longer be available, and one of the two would have to be relocated because the room dimensions were made very tight. But that is only theoretical in a sense, as from my point of view this design is already dead, as I have already hinted:

I don’t quite understand what you mean. The OP wants a log house. Why do you want to persuade them to go with Ytong now?

A standard house is already planned and implemented dozens of times; there are fewer pitfalls

I had certainly noticed the OP’s desire for a log house, but equally also the budget reservation, the ability to enforce the decision in favor of a “wish-come-true” house. Mind you, I did not suggest a standard house here, but explicitly a kit house, namely from the catalog of the system supplier (although I have not checked whether the kit house catalogs from Xella actually differ between the Ytong and Hebel brands). In any case, the kit house expressly aims, deviating from the general standard house, not only to save the design architect as desired, but explicitly to receive a package with precisely counted little bags of stones, which makes the total price the most calculable. In addition, aerated concrete can be processed foolproofly, so the only thing missing from a Lego-kit is really the studs on the bricks. For formwork stone kits it would be similar in this respect, but secondly their suitability for laypersons is lower, and first, they are not so compatible with “commonly trained” craftsmen who are not specifically experienced with exotic materials. For the same reason, I did not even bring alternatives like GreMagor or similar into play here. Likewise, I treated Massa Haus and the like; instead, I explicitly proposed 1. a kit house and 2. its mixed general contractor and self-performed construction. Don’t forget: I am not “just” the funny architect-swearing uncle, but also do independent homebuyer consulting professionally. The means of bursting dream bubbles is therefore sanctified by the purpose of being able to strive for a realistic successful feasibility on the ground.

By the way, the log house in this case is only a "log" house: the log house construction method (also with the logs) has been long dead since the beginning of the Energy Saving Ordinance / Building Energy Act era, because it is no longer possible in the classic form. And those fake dovetails, like those here on the facade continuing the sandwich “logs” merely clad with wood visually, can be slapped onto any other Scandinavian-look facade. The costs for this design gimmick are, by the way, the same on houses of classic construction methods. If I got a mark from every victim of such exotic alternative example calculations, I could fly to the bakery by helicopter. But to each their own (those who wake up in time, however, I am happy to help).

I have looked at the orientations again and with the two additional (elaborate) gables and the access path, it makes sense to me to use the gable on the north as the entrance. The roofing (roof) there should be used for the entrance. Also, I would extend the living area around the corner, that is, swap the utility room and the living room, put the dining area in the southwest. The WC then goes to the east. You then have a nice southwest orientation and a good zoning.
Additionally, there is a nice sightline from the entrance to the terrace.
The utility room is still too big for my taste… I have seen 6 sqm small rooms that had a lot of storage space and work surface on 3 meters length thanks to a kitchen unit, with shelves on the other side. Ok, there was no drying area included there.
I still see it very positively that you have put some thought into it. Overall, it is much better than the first draft. House plans should grow and one should try out a lot. Maybe your husband will play Tetris again and experiment a bit?!
I cannot say anything about log walls and the like.

I still see it very positively that you have given it some thought. Overall, it is much better than the first draft.

Yes, and this praise retains its value even if one decides to completely forgo a redesign. Because even a mere redesign already leaves the safe harbor of a proven draft, and every complication (removal) causes additional and basically worthless costs.

The utility room is still too big for my taste…

The shortest (and also the most appropriate for the house size) way out of the dilemma of the combination "too large utility room and too small entrance area" is the merging of both functions into a shared room. If you then cut the tether coupling utility room / carport / side entrance into a devil’s triangle, the positioning of the building gains decisive freedom.

I stand by this: Wolperting is a district of Cloudcuckooland. You cannot want to forgo any of the wishes (log cabin look, individual planning, priority on optimizing the side entrance) OR fulfill your building dream affordably within the framework of the Kreisliga B (Town & Country flair or similar) with only mildly painful compromises. I do not see this succeeding with AND linked, even if the exotic alternative sellers are only too happy to sell you this bear.