Which house can we afford? The land exists

I'll take a look into my crystal ball.

Construction in 2022:
170sqm * 2200 = 374k
Usable basement: 70k
Masonry double garage: 30k
Additional construction costs: 30k (for level plot)
Outdoor facilities: 25k
Kitchen and other furnishings: 25k

Therefore, I am of the opinion that you need about 450k just for the house including the basement.
Additional construction costs, garage, outdoor facilities, furniture, and special requests come on top.

Why didn't you finance the plot flexibly????

If you already found Bien-Zenker and Weberhaus quite nice: just request offers directly from Bien-Zenker and Weberhaus. Read the construction service descriptions carefully and make a list of what you want on top of the standard.

Otherwise, as a rough estimate you can calculate €2000-€2500/m² + garage + basement (dependent on region and soil; get offers, ask in the municipality/neighbors, etc., if they can assess the soil a bit) + ancillary building costs + exterior landscaping + kitchen.

And discuss once more thoroughly how many m²/rooms you need. 170m² including office, guest room, 3 bathrooms, utility room and garage is already a lot of space and a lot of costs PLUS basement -> what for the basement? Only storage space? Can rooms then be moved out of the house (utility room, anything else? You don’t need 90-100m² basement just as utility room and storage space, that will probably be too expensive).

Good luck

What on earth possessed you to take out a mortgage for a plot of land that you could have simply paid for in cash? Who advised you on that?
Complete nonsense, now you're tied to the bank...

As mentioned above, no, with 450k there is no 170m² house with a basement and double garage.
With a basement, 150m² should suffice, that works, even with a study.

What on earth made you take out a mortgage for a plot of land that you could have simply paid in cash? Who advised you there? Complete nonsense, now you are tied to the bank...

As already said above, no, for 450k there is no 170m² house with a basement and double garage. With a basement, however, 150m² should be enough, that’s doable, even with a study.

Unfortunately, I thought the same at first! The bank doesn’t have to make any effort for the main loan now! They can also just write down 3%. Well, whatever. With land and buffer you end up at a 600k loan, if children come along with that income... for me, that’s too much

Does anyone have experience with whether it might be possible to convince the bank to convert the loan into a variable one? Variable to fixed is no problem ... but the other way around? That would be a chance for you to flexibly use the market for the home loan and not be dependent on the current bank.

Unfortunately, I thought the same at first! The bank now doesn’t have to make any effort for the main loan! They can just write down 3%. Oh well. With the land and buffer, you end up with a 600k loan, if children are added with that income... for me, too much

I think they will manage with 600k costs if they don’t go overboard with the construction. Then over 100k equity. That’s 500k loan with over 7k net per month. Where is that too much or a problem?