Is the financing plan realistic?

3 thinking errors, just to be seen as a hint:

I get an average annual raise of 3% and my wife does too (over the last ~5 years).

Raise = inflation adjustment = compensation for higher living costs

If I take our current warm rent of 1000 + 600 (800 - 200 for car),

You must not use the warm rent, only the cold rent.
Electricity consumption in a house is usually more expensive than 40€, heating is also necessary, furthermore, there are additional ancillary costs such as waste, water, property tax, etc.

Why does the house cost more? We have concrete offers for turnkey houses.

I don't see any additional construction costs in the calculation.
My predecessors correctly mention here the hardly calculable earthworks as well as the fact that there are very few providers who consider the word turnkey to mean ready to move in. And if they do, they also state it.
The rooms hallway/kitchen/bathroom are equipped with tiles, the living rooms are added at the builder's expense.
Also, a low house price results if not all services that one expects are listed in the construction service description.
Everything that has to be done on site must be additionally done by the builder themselves -> commissioned and paid for by themselves.

Salary increase = compensation for inflation = compensation for higher living costs

In connection with an annuity loan, this is IMHO not a misconception. The higher the inflation (but please not as a shock!), the better, because the debts can then be paid off more easily. The annuity initially remains constant, but its share of the disposable income decreases. That is good! But(!!): A bad financing will not become good through such hope. I fully agree with you on all other points!

We aimed for a loan repayment of approximately 1000-1100 monthly. The rest would then be for ancillary costs/savings.

We have already been to 3 local banks and a rough financing plan was made, and all said that it is realistic and affordable (for about 35 years at a fixed interest rate. Of course, that probably won’t remain the case, but I think possible increases could be offset by salary raises). But those are banks and somehow I don't really trust them.

Regardless, some things are not yet included in the calculation. Did any of the 3 banks offer you the 335,000 you estimated for 1100€ per month, or present it as feasible? Or where does this land?

The problem I see is either the proposed fixed interest rate terms are quite short, or the repayment was set very low.

Mathematically, you would need to get a blended interest rate of 1.93% or better (which is not so easy anymore, since the KfW raised interest rates significantly 2-3 days ago), or at least start with 2% repayment; assuming you want to finish with 1100 in 35 years. 1100 is only 3.9% annuity.

At the moment, one aims for as long a fixed interest rate term as possible (preferably 20 years) or a high repayment rate. But that is not possible with 1100 for the amount you have estimated so far (which actually everyone here feels is too low).

Personally, I would not approach the project with less than a 5% annuity (interest + repayment). In your estimated case, that would mean a burden of about ~1400.

In connection with an annuity loan, this is IMHO not a flaw in reasoning. The higher the inflation (but please not as a shock!), the better, because the debts can then be repaid more easily. The annuity initially remains constant, but its share of disposable income decreases. That is good! But(!!): A bad financing does not become good because of such hope.

In all other points I fully agree with you!

If I understand you correctly, you are right

As I understand the OP, he expects more cash flow, which enables him to spend more money on himself...

Ok, then asked differently: What costs per sqm do I have to expect for an approximately 130 sqm house (at least KFW55) with standard equipment?

Really everything complete (foundation slab, all necessary work on the property, as well as inside - only external facilities not included). The property would cost 85 euros per sqm (727 sqm) plus purchase additional costs and all connection fees.

In my offer, I would be at 2076 per sqm (272,000 / 131). Will it really be that much more expensive? Honestly, I can't really imagine that, but of course I have no experience. But what I've heard from acquaintances is roughly about right.

You watch #9
With calculation, you are not wrong

Greetings