Massive house construction with a basement and a granny flat affordable with 340k financing?

Hello, I hope this is the right place, if not, please move it. I am planning to build a house and am still doing a financial check. I ask for your help on how realistically you assess the house construction and whether the basement (as I fear) is financially not feasible. Appointments with builders are coming up.

General information about me:

[*]Single parent, 38 years old, two children, employed full-time + side job

Income and asset situation:

[*]net 3000, 400 child benefit
[*]equity: plot of land 800 sqm
[*]I currently live in a house paying about 600€ repayment/interest, would rent it out for a similar amount, so I would have 600€ monthly. Additionally, I have about 800€ "left over" each month that I invest in improvement work on my current house.

General information about the property:

[*]Land available, carport instead of garage planned
[*]House should have 2 floors ground floor 77 sqm, upper floor 70 sqm, basement if possible also under terrace with 130 sqm
[*]House should cost about 340,000 "turnkey".

Construction or purchase costs:

[*]Development costs about 8000
[*]Soil surveyor, trees, etc. 7000
[*]Outdoor facilities/terrace, paths, garden design, fences etc...40,000

Other costs: Kitchen costs: 10,000. furniture, lamps, decoration: 5000
Cost summary:

[*]Financing amount 400,000

Necessary loan details:

[*]Loan amount 380,000 annuity loan (of which 100,000 KFW 3 years repayment pause), soil survey from own funds in advance, kitchen/furniture installment loan, which is paid off in the first 3 years. (I did it this way with the current house as well.)
[*]Fixed interest term 20 years (or KfW part 10), total term 30 years. (KfW 20 years)
[*]monthly rate after 3 years: 980+450= 1430€

Main issue:
The house should ideally be completely basemented, possibly with a granny flat in the basement. It would need to be a WW because of high groundwater. And it should be an elevated basement.
If with a granny flat, there would be a "shared" basement entrance, which alone would probably cost me 15,000-17,000€.
Question: My budget is 340,000 for the house.
Option 1: I build completely without a basement.
Option 2: I build with a partial basement.
Option 3: I build with a basement under the house, but not under the terrace without a basement door.
Option 4: I build with a basement as planned but without a granny flat and without a basement door.
Option 5: I build with a basement as planned, with a granny flat.

The floor plans were created by me by hand or [ATTACH alt="front.jpg" type="full"]53810[/ATTACH][ATTACH alt="keller.jpg" type="full"]53811[/ATTACH][ATTACH alt="og.jpg" type="full"]53812[/ATTACH][ATTACH alt="quer.jpg" type="full"]53813[/ATTACH] on the phone and are not very precise, I know, it is just supposed to be an idea. The kitchen corner is in the east, the living room corner in the west. The picture is also just an idea of which direction it should go.

Thank you very much in advance.

No budget too small

ok thanks, I suspected it

Hello, I don't quite understand your calculation. You don't actually have the 600€ rent available, but you still have to put it into the loan. That means you only have the 800€ for the new financing, right? Until when is the old house paid off? Is a sale out of the question?

Option 1 without a basement could be possible. But as a single parent with 2 children, a lot of personal effort is out of the question. Why do you want to put yourself through that?

The budget is too low for the basement. You have also forgotten quite a bit in the incidental construction costs. Where are, for example, the costs for excavation? With a basement, that can quickly be 25-30k.