Does my budget fit the construction project?

I had Elterngeld Plus, it is great when you work part-time You only listed the 1800 euros for 12 months for your wife And then only 2 months or 4 remain for you Have you ever calculated the partner months. Both part-time?

It's already calculated a bit tight. There will definitely be at least 50k more on top (probably more).

The basement as a usable cellar will probably cost closer to 80k.
Earthworks are completely missing in your calculation. 25k is no problem including removal of the cellar excavation.
Outdoor facilities are also tight. You’ll only manage with 15k if you do everything in EL. You also have a slight slope. Do you need L-blocks anywhere?
Double garage is also tight. Even as a prefabricated garage. If you imagine something built from masonry, even more so.
Kitchen, furniture, etc. is tight as well.

I rather come to the following calculation:
Land including notary 157k
150 sqm living space 300k
Basement 80k
Additional building costs 30k
Earthworks 25k
Double garage 30k
Kitchen, lamps, furnishings, etc. 25k
Outdoor facilities 25k
Total thus 672k

Which means roughly a 450k loan. But that should be doable with your income. 1700 EUR installment is also about right.

My goodness, I could have written that a bit more precisely. Should I apologize for that now? Whether I get 900 bucks for 4 months or 6 months doesn't make a difference for the question. Yes, the partner months are also quite nice, that would be 2 months more if I remember correctly. Somehow we didn't really respond to that.

I have increased the calculation for the garage to 30k and the kitchen + a few pieces of furniture (we already have most of the furniture in the apartment) to 25k. The basement is getting more expensive with every post, I don’t want to sugarcoat things, but also not go overboard. In the end, I’ll need a reasonably reliable offer anyway before I finalize this with the bank, so at this point it’s not that important whether it’s 60 or 75. Maybe it will even be a slightly smaller garage and an additional covered shelter. The plot is not completely flat but with about 1m elevation difference also not a steep slope. I don’t think much support will be needed there.

Well, but did you think you would get a 75sqm cellar for 50k including excavation and removal of the soil? Should the cellar be inside or outside the thermal envelope? Should the technology go down there? Should there be a room that can be heated (hobby room)?

I am certainly capable of learning. If the general opinion here says a basement costs 80,000 then I don't say it can't be. Yes, a technical room for heating and such should be in the basement. Heated rooms actually not. Possibly a room with the [Lüftungsanlage].