Is financing a single-family house feasible for us?

Do you have a soil survey and reliable information about the disposal costs for the basement excavation? That would help to defuse what is often the most expensive additional claim.

That would also be my first measure. Soil survey and planning based on it. Groundwater and construction measures that urgently need to be included based on the survey. Have the Z-value determined and get EXACT offers from the landscaper or whoever will be digging the hole, including disposal.

Urgently calculate things like possibly necessary drainage or watertight concrete (WU concrete) during the basement work. We are building on "biosand" and it even seems to be slightly cheaper than originally planned. But we probably caught the absolute exception there.

Your planned value is close to what we pay. But as I said, for completely problem-free and uncontaminated sand, which others would envy for filling or something. In your case, it can actually only become more expensive!

We have the soil survey and the excavation volume is definitely sufficient. Frost protection gravel for backfilling is more difficult to check for a layperson.

Overall, it does frustrate me that despite being economical and hardworking, you can't build an 8x10 house with a basement on about 300 sqm of land.
If you leave the garage aside, those are not extreme requirements up to that point.
We will probably have to adjust our wishes for the interior finishing as well, then hopefully it will work out.

Oh wow, with parents as the construction crew, I can imagine some really dreadful scenarios, but since I don't know your parents, I assume you have thought it through carefully. It is definitely an advantage if someone can supervise the construction site almost around the clock.

Overall, it frustrates me that despite thriftiness and a lot of diligence, you can't build an 8x10 house with a basement on about 300 sqm of land. If you leave the garage aside, those are not extreme demands up to that point. We will probably have to adjust our wishes for the interior work again, then hopefully it will work out.

You can build your house – you just can’t tick every single wish off. "We'll take everything, you only build once" just isn’t possible. I would prioritize the wishes, both by the necessity of the wish and by the possibility of retrofitting. Retrofitting a basement – difficult. Retrofitting a garage – easy. Expanding outdoor facilities – easy. Changing windows – possible but annoying, especially if the size should also be changed. And so on. Clear consequence: build the basement, the garage according to budget, when the rest is mostly finished. Some things can be prepared (empty conduits, connections already laid, etc.) for little money so that later retrofitting doesn’t require major alterations to the existing structure. Use these possibilities consistently. Otherwise, again as a fallback: my parents also like to help a lot. Actually, sometimes financially too, but they get that back. I just find it concerning if you fundamentally cannot manage without their help. Because they can get sick too, so that they simply are no longer available. For example, to look after the children. An acquaintance of mine has a husband who specialized as a contractor in the renovation of very old buildings. He worked nationwide, rarely/never around during the week. To be able to pursue her job, she had an almost different "borrowed grandma" every weekday (e.g., on Monday Berta picks up the child and on Tuesday Hilde, etc.) because she rarely managed to leave work early enough to make it for kindergarten closing. Such a thing is very difficult in my eyes. If Hilde or Berta or Gudrun get sick... then it just doesn’t work anymore at first. In fact, her husband eventually gave up on monument renovation and started working regionally again. PS: I have a similarly small plot and a house with similar external dimensions. I simply can’t imagine fitting such a large garage on the plot as well, no matter how hard I try.

That sounds very reasonable, what you are writing. If my better half also sees that, then it will work out. You are completely right about the parents. That’s why it is actually planned so that it can work without them. Since our building window for the house is fixed and the garage is attached to the north of it, we don’t lose any other reasonably usable space because of the garage. Otherwise, it would just be a driveway or a small front garden. To the east, south, and west, we each have exactly 3 meters to the neighboring property and that cannot be changed. But as I said, I will definitely take a red pen to the garage. First, move it backward and secondly, it really can be smaller... We took over the size of my parents’ and didn’t think the financing would be so tight :-(

Second child we might actually find less important than the basement at the current state.

This comparison is really very pathetic. Very.