Financing land and house? Taking out a mortgage? Construction costs?

I also find the cost framework "normal". Savings potentials were already mentioned: windows; floor coverings (there the price differences are huge); kitchen (here too the price is very open upwards). What I also don't understand is why you didn't invest more equity in the building plot: for own money, there is currently practically nothing on the market. But for borrowed capital you have to pay 1.1%. Therefore, always "need" equity first (of course with a reserve). But the die is cast.

I know a female architect, and she built in a down-to-earth manner. She calculated several times whether an extension of the house by one meter was affordable. I find it silly when people take the glossy standard as their own, even if they are professionals. What drives up costs here has already been pointed out by others. You build what you can afford yourself and not a prestige project of the star league. Sorry, a bit exaggerated ... should just be an example. Apart from that, I see quite a bit more cost with tiles if you move into the mid-range.

Tiling is actually done very little, hence the total.

Nordlys, by the way, we drive Skoda

Thank you very much for the suggestion regarding the garage, we have also considered that. Too long, but standard size and prefabricated garage. Unfortunately, it has to be built on a slab due to regulations in our case. And the excessive length was mainly planned due to the lack of a basement, but then a shed will have to be added in two or three years.

Although I still have stomach pains over the high amount, the bank will probably have to calculate what the monthly burden will be. Currently, I am getting a retroactive salary increase of 100 net from January 1st, and then again in 2020 (thanks to the collective bargaining round)...

I also find the cost framework "normal".
Potential savings have already been mentioned: windows; floor coverings (the price differences here are huge); kitchen (here, too, the price is very open upwards).

In my opinion, very little can be saved on the floor coverings when only 12k is budgeted.
As already noted, the windows item is actually the best item to save on. Wood-aluminum is more than three times as expensive as plastic.

But, with 6k net, building the house should be possible. The additional need for the land charge is simply recorded by the notary and that's that.

I really know many people who build huge houses with basements that don’t end up costing more... (Sure, probably a different standard)

But I seriously doubt that now. Anyone who has built what you call "huge houses" in Bavaria within the last 2-3 years has definitely paid a lot. Either the houses are older, so you can’t compare because of the boom. Or people aren’t telling you the real numbers, which – even among friends – is pretty standard when talking about building a house.

Well, the train with the equity has left the station. I would have found it better invested in the plot of land anyway, because there’s certainly no less value there than the measly interest on a savings account. Increase in the equity value in the land is better/never worse than in the bank account.

The thing with architects planning their own homes is like doctors being patients at colleagues’ practices. Not always result-oriented. For your standards, the price is not high, but okay.

Currently, I am receiving a retroactive salary increase of 100 net as of January 1st, then again in 2020 (thanks to the collective bargaining round)...

It's a bit off topic or maybe not:
Collective bargaining round in the public sector? Then your gross must be over 5000 if you get 100€ net. Is that so? Then your husband as an architect earns less than you, if you have 6000 net together?