Land purchase of 319 sqm for 191,000 euros and house construction realistic?

How many working hours have you actually planned for the interior finishing and in what time period do you want to accomplish that? In the meantime, you are paying rent or living on a construction site. And even if 35 hours is not much: if you don't live very close to the construction site, realistically only the weekends remain mostly for the finishing.

What special finishing? It’s supposed to be only the usual things like painting/sanding, laying floors or other small stuff. That won’t take months. Realistically, you don’t need more than a few days off and the weekends.

Alright, I only have experience with renovation. The dismantling is naturally out of the question. But plastering (instead of wallpapering) or installing drywall sheets didn’t go that quickly either.

Maybe a few more points regarding the additional costs:
- Bauleistungsversicherung ==> for construction with a general contractor please have the general contractor take out the insurance directly, it is not your responsibility
- Baustraße ==> as mentioned, not necessary
- Prüfstatik ==> if nothing has changed in Bavaria, for a single-family house whose structural analysis is done by an authorized expert, no Prüfstatik is required
- Connection of electricity, water, telecommunications, etc. can be inquired from the utility providers
...

Please do not simply take any numbers and items from the internet.

Well, I only have experience with renovation. The dismantling is of course out of the question. But plastering (instead of wallpapering) or installing drywall panels didn’t happen that fast either

Just for clarification: Drywall in new construction only in EL if you want to lower the ceiling (for whatever reason – serious reasons are very rare, usually just a "want to have"). Otherwise, the walls in prefabricated houses are clad by the company, in solid construction plastered by the plasterer. Afterwards, depending on the agreed quality level, further refinement and sanding + wallpapering (nowadays rather painter’s fleece) + painting can be done. Solid ceilings are either plastered as well (almost everyone in my region does this) or puttied, sanded and painted. Also no rocket science.

That won't work, unless you want to live like a low earner for 10, 20 years. Especially since your calculation doesn't include furniture, kitchen, or landscaping. Because seriously. 2,000 EUR for the garden? 2,000 for a fence? You can hardly get the necessary tools for that, let alone materials. Why no construction period interest?

(...) Not rocket science either.

If you take your time or are satisfied with Q2, no. Anyone who as an amateur wants to achieve Q3 and finish in a limited time, good luck.

I plastered and sanded 40m² of a living room concrete ceiling. The result is so-so, but I will never put myself through this torture again.