Semi-detached house, upscale fittings: Are the additional costs correct?

Why? Because it is simply beautiful.
By the way, this also applies to the vacation you mentioned or the car most of us drive (only a few drive the cheapest car). Nobody needs it, but everyone has it. Internet to be active here in the forum? You don’t need it either and it just costs unnecessarily hard-earned money.
Let’s just have our fun

P.S. Great equipment in the house and otherwise still a nice life are not mutually exclusive, but fit together...

In my circle of acquaintances, many people say they want to get from A to B by car. It is exactly the same with the equipment of the house. The question is not what is usual, but one's own priorities. Upscale equipment will, just like additional insulation or a heat pump with controlled residential ventilation, rarely pay off financially. It depends on one's own needs and the financial resources available.

Well, with something like tiles, I also wonder why you have to use such expensive tiles. But that's a matter of taste; if you like cheap tiles best, then you should take those and not ones twice as expensive just to have an upscale finish.

A brief note from us on the subject of tiles:

We also did not have super-duper expensive tiles installed. However, we installed exactly the tiles that we liked.
Only the tiles for the utility room and the storage room would fall within the budget of 18 euros you set (about 13 euros).

The contract specified 25 euros/sqm (including VAT). However, we were aware that we would likely exceed that amount due to the selection, so we factored in an additional sum from the start.
In the end, we averaged 35 euros/sqm (except for the bathroom wall tiles) and are more than satisfied with the selection. At one point, tiles at 59 euros/sqm were even considered for the living room. However, we then found some that we liked better and that cost about 39 euros.

We were also on average at about 35 euros per sqm, some were much cheaper, but the large areas were somewhat more expensive.

Has a soil survey been done in the meantime?

From our own experience, we can only recommend it. We also have a stream at the end of the property, and the "strained groundwater" became a problem. Additional foundation costs are often only planned up to €5,000 by the companies. In our case, the additional costs were exactly €10,587 higher. A nice small sum that can be hard for you to manage if you calculate too tightly or if the developer included an exact amount in the contract that he himself bears.

Please don't misunderstand me, but when reading the last two threads, I increasingly got the feeling that you haven't first read up yourself or seriously inquired. It is not enough to rely on the opinions of others. You must acquire basic knowledge yourself. This is missing, considering, among other things, the question regarding ETICS or about KFW. Have you ever visited construction fairs or consulted with very different developers? What does your house bank say? ......

Have you asked the owner of the property yourself if she might sell you the property at a good price? Then you are independent of the developer. But have a soil survey done first! Depending on the result, this can also reduce the purchase price.

Many people dream of owning a house! Preparation and information in advance are important. Reading and comparing various construction specifications should definitely have been done.

Good luck with that!