House construction planning

You have written quite a lot here ;) I'm always happy about comments, but everything should always remain constructive and not offensive. I'll see if I can find the subforum ;)

Otherwise, I think the developer option is off the table because we plan to buy the plot from the municipality....so then general contractor / general contractor with services. As I said, the first things have been set in motion, now waiting for feedback...

Regarding our expenses:
€650 rent including utilities
€70 electricity
€30 internet
€150 insurance
€400 cars
€20 mobile phone
€400 groceries
€500 miscellaneous
That should be the main part. Loans are not to be repaid.

How much credit would be expected here under what conditions? Is it even possible to finance a house with this?

Can someone comment on this?
If you buy a plot from the municipality in a new development area, it should be fully developed, right, or do further surveys or similar need to be carried out?

It always depends a bit... so as a rate you have about max. €1400 available – the rent will no longer apply, but the additional costs will increase. However, then you would have little buffer. I would rather set about €1200.
The land is then paid off, if I understood correctly – anyway you will probably have a loan-to-value ratio between 80 and 90%. Let's just assume 2.5% interest rate with a 15-year fixed interest period. From that, a maximum house price of about €320k at 2% repayment or €260k at 3% would result.
Even with acceptable fittings (€1600/m² in ST) you should be able to finance the 130 sqm with both scenarios -> €1600 *130 ~€210k + €50k additional costs -> €260k.
Of course, you have to know whether you stick to your expenses and income!