Dream plot, but TAFF house - first mistake already made

I have the construction service description available, just don’t know if I’m allowed to post it. The staircase, for example, is described as follows: "Steel two-stringer staircase made of rectangular tube (60x40mm) with rust protection coating."
It also states that it will be covered with construction treads, mounted acoustically decoupled from the building structure, and that any parapet railings (with exact designation/dimensions) will be installed.
And of course, that the "shell staircase can be turned into a finished staircase by replacing the construction treads with new, site-delivered treads and risers," which costs extra.

For electrical work, I have the switches, number of sockets, and additional boxes (network, antenna, etc.) booked for each room.

For sanitary objects, I only have the exact number and type as well as a general description: "For the sanitary fixtures, products from brand manufacturers (Duravig, model series D-Code, white) and fittings from Grohe or equivalent are used." Equivalent is somewhat vaguely formulated here for me. Allegedly, a lump sum price is set for this level of equipment, and you can then choose something from the catalog which may be more expensive or cheaper. Allegedly, you can also buy everything in Poland and have it installed on site if you want to save a lot...

The same applies to the tiles; you can basically choose everything up to the stated 30€/m².

I have to say, the more I read through this, the more serious the whole thing sounds. Now it’s important to clarify the uncertainties in the contract/construction service description and check that everything is included in the offer. I already have quite a few notes and questions...

However, in my opinion you won’t make yourself happy with the first available plot, which on paper looks more like a nightmare.

Nightmare? Because of the former workshop now?

There’s no rush for you anyway, there are still more plots in Saxony than elsewhere.

That really depends on the location. In our case, it’s unfortunately not just a broker’s invention that (affordable) properties and plots in the area go like hotcakes. One third of our potential "candidates" were already gone at the time of our inquiry.

For tiles and floors, you can ask for more than double that amount. For the included price, there is only the lowest hardware store standard.

I would have to look into that more thoroughly. I immediately found some tiles in the price range that I would like. What speaks against inexpensive tiles or, in your opinion, what would be a "decent" tile? Or flooring. Poland is always an option too...

And of course, that the "shell staircase can be turned into a finished staircase by replacing the construction steps with new risers and treads supplied on site," which costs extra

bauseits means bought and provided by the builder. But I find that quite something: the house isn’t cheap at all – but that not even a living staircase is installed is outrageous. By the way, we have such a staircase, it was standard too, we still had to paint it and we changed the wood as well as added risers.

Duravig, model series D-Code, white

Duravit. You have to like the model – it’s also not exactly the latest model.

bauseits means purchased and provided by the client. But I find this shocking: the house isn't exactly cheap – yet not even a residential staircase is installed, which is outrageous.

The construction service description outlines the base price. I simply assume that the finished residential staircase is listed in the offer under "Interior staircase finished steps with installation" at €2200, so it is already included in the total price. However, I am missing the details on the stair treads, such as material and thickness. Another assumption: this is a flat rate and depends on exactly what we decide on. I will definitely clarify this.

Duravit. You have to like the model – it’s not exactly the most current model either

I checked again, it’s not particularly attractive. However, the offer includes the higher-quality package, meaning we can rely on the blanket statement here:
Higher-quality sanitary fittings will be supplied and installed. For example, toilets will be delivered rimless with nanocoating. Fittings from Hansgrohe (Focus series) or equivalent. That sounds better, although still a bit vague. Presumably, TAFF doesn’t want to update the text constantly.

Would you consider this in the situation as well? Are there risks?

As you describe it, I would under no circumstances sign any contract with this broker and this company. I wouldn't even buy a used car from them. Let alone a house.

Either you can buy this plot of land directly from the owner, without developer or general contractor compulsion. Or you find another plot (free of developer) or a reputable developer (one or this strange hidden model).

I immediately found some tiles in the price range

At the hardware store? Or in the sampling from Taff? Don’t forget that almost every house provider does not charge you the pure material prices.

What strikes me about your costs is that, for example, the house connection costs are very tightly budgeted. In addition, depending on the local conditions, either rainwater infiltration or sewer connection fees apply.

The material prices listed for tiles and the other floors would now be considered low quality here. You have to want that.

What about the security of the windows and doors? Are there mushroom heads included?

What about the garden and outdoor areas? Terrace?
Entrance steps? So far, you can only enter the house via 2 Euro pallets.
Garage? Carport?
Lighting in the house?
Kitchen?

Buffer for contingencies?

Have you left room in the budget for all the aforementioned things, or are they considered secondary? So, besides the plot, the land transfer costs, and the house price, do you still have around €60,000–85,000 left in the budget?