400k house estimated - became a 470k house / an experience report

Thank you for the experience report!
It is not called for nothing: The dream of owning a house.

Who wants to settle for tiles they like second best, the cheapest and least comfortable heating or ventilation system, second-choice bathroom furniture, etc.?

You quickly realize: This will stay inside forever, so I choose quality and what I like best here!
That is how it went for us, from the real wood parquet to the kitchen.

Did I miss it? How far along is the house construction?

You haven't missed anything. So far, nothing more except the information from the opening post.

Thank you for the experience report! It’s not called the dream of owning a house for nothing. Who would want to settle for tiles they like second best, the cheapest and least comfortable heating or ventilation system, second-choice bathroom furniture, etc.? You quickly come to realize: It stays in there forever, so I’ll choose quality and what I like best! That’s how it went for us, from the real wood parquet to the kitchen.

But you have to be able to afford this attitude first.

This can be seen in an Excel table, in which all costs and special requests +5% are listed

you can see this in an Excel table that lists all costs and special requests +5%

And the opening post says exactly the opposite. That’s why we came to the topic, which roughly means: how do I stay within the budget and can build cheaply (NOT cheaply!)?
Special requests during the sample selection easily add up to 50k. That blows some calculations out of the water. Electrical work not agreed and signed before contract conclusion? Well, 6 sockets in the living/dining room as standard. Each additional socket = 100€. You often read this here and it’s surely often forgotten. Almost no one manages to calculate EVERYTHING consistently realistically. Here the drainage was forgotten, soil replacement wasn’t in the plan, etc., etc. Then “you only build once” and naturally take the expensive kitchen. You have to plan that early so it fits. Oops 25k instead of the planned 15k. And so on and so forth.
And that’s exactly what the OP is describing here.

That doesn’t say the opposite at all! You can also feed the Excel with additional costs for desired special expenses or higher-quality materials.
For example: 100 sqm laminate: 2,500,- vs. 100 sqm parquet: 6,000,-
This way you can see in the end where the budget is going and what you can afford and what you have to cut.
But you shouldn’t have to tell that to anyone who plans to build a house. That has to be at the top of the to-do list!
The OP probably didn’t decide on KNX without knowing beforehand what a hole that would put in the budget.