Is our house construction project realistic?

Regarding 2)
You can only say that once you know the house. How much space will be enclosed, possibly the gallery can be changed/the house can be downsized without any loss of comfort.
About 3 years ago, we were offered a staggered shed roof house, approx. 135sqm with gallery ... by the GU for 150,000, with Kfw70, controlled residential ventilation, and various additional features just under 200,000.
However, we have different prices now than three years ago, the house is not known (maybe really much more elaborate), and NDS is not RP.

For 250,000 you get a house with 160sqm, your calculation is missing the exterior facilities. I consider 50,000 for a plot of land a bargain, on the other hand ;)

I will schedule an appointment next week with a [GU] who was recommended to us several times. Afterwards, we will see what needs to be cut... There are also some plots of land here for less money :). The outdoor area can be handled by my best friend (landscape gardening) and is therefore not forgotten - but hopefully it will be affordable ;)

I now consider €290,000 for a turnkey house including all additional costs completely unrealistic. We also want to build in rural RLP. We are planning about 160 sqm of living space as well, but "only" with a normal gable roof. According to our research, a reasonable standard with a reputable general contractor is hardly achievable for less than €220,000. As a rule, these prices usually do not include floor and painting work. If you also want the general contractor to do that, I would calculate at least €30,000, rather more. At that point, you still haven't made any upgrades, and there will be additional costs there as well. I think no one is satisfied with the absolute minimum standard in every area when it comes to such a life project. And no matter which general contractor or individual architect you go to, you will have to reckon with additional construction costs of €40,000-50,000. You surely want outdoor facilities as well; we were given an average realistic estimate of €100 per sqm for that, depending on how you want them designed. It can certainly be considerably cheaper if you can do a lot yourself. But €290,000 for turnkey in the sense of absolutely everything finished, upgrades, shed roof, gallery... I think you can rather forget that.

We would take care of painting and flooring ourselves (except for the bathroom and guest toilet). I would initially design the outdoor area quite minimally, that can also be done later.

Basically, I also assume that we will not get the desired house at this price. If it then becomes 150 sqm with a small gallery or, if necessary, without one, that is not the end of the world! But I read somewhere that a "simple" shed roof is cheaper than a normal gable roof. However, that might also be misinformation...

Best regards!

You probably want landscaping as well, and as a reliable benchmark we've been given an average of 100 € per sqm, no matter how you want it designed. It can certainly be much cheaper if you can do a lot yourself. But 290,000 euros for turnkey in the sense of everything everything finished, pattern layouts, shed roof, gallery... I think you can rather forget that.

That is probably a bit exaggerated.

What is planned for 10,000 € for 100 sqm / 40,000 € for 400 sqm garden portion of the property? Gilded stepping stones? Bonsai trees as a hedge?

Of course, it might be exaggerated. I have very, very little knowledge about costs for plantings, paving + labor, fencing with a fence, stone wall, lawn costs... The value was given to us by a general contractor, and we also think that you will probably get by with it. In case of doubt, I prefer to calculate a bit more generously, and if there is more left over afterwards, all the better.

Regarding painting and flooring work: Even if you do a lot yourselves (offsetting the costs, you might also have to take vacation, etc.), you still have the costs for the materials.