Single-family house + land (purchase or leasehold) with high interest rates

Hello,

we (wife, 2 children and I) are currently planning to build a house.

Key data:
Single-family house costs approx. €420,000, KfW 40+
Plot €110,000 + ancillary purchase costs without realtor
Equity €92,000

Income €3,200 net + €438 child benefit
My wife currently receives no salary, therefore not included
My employment contract is limited until 2022, as I changed the workplace in 2019, I work in the public service, not a civil servant.

We could buy the above plot or have a leasehold plot from the employer.

I have received offers from banks for the case with leasehold.

For the leasehold plot, I would still have to pay the street + sewer fees totaling €32,000.

Offer from the cheapest bank
€365,000 30 years fixed interest rate, 1.8% nominal interest, 1.83% effective, €1,150 monthly rate, no KfW, 18 months availability

Are the interest rates so high because of the limitation?
Is there any way to reduce them?

Are the interest rates so high because of the fixed term? Can they be reduced somehow?

2x no. In the very long-term area, the price is okay.

Does anyone actually know how the subsidy from the Kfw works starting in July? Apparently, you are supposed to be able to apply for the subsidy without a loan. How is it calculated? For the loan, it is percentage X of loan amount Y.

We want to build a single-family house with a finished granny flat. Then we would have to get the kfw 40+ subsidy twice, but at what amount without a loan?

For the leased land, I would still have to pay the street + sewer fee totaling 32,000€.

So that means the purchase plot effectively costs you an additional €80,000 because the development is already included then?
In this case, I would tend to lean towards buying, provided the leasehold interest is not extremely low (you would still have to tell us that, otherwise we can't give any advice).

We want to build a single-family house with a developed granny flat. Then we would have to get 2x KfW 40+ subsidies, but how much without a loan?

The subsidy is per residential unit. I think it will be the same amount as the repayment subsidy with the loan. Anything else doesn't really make much sense.
Important for the subsidy variant is that you do not sign a construction contract before July, otherwise only the "old KfW" applies.

Are the interest rates so high because of the time limit?
Is there any way to lower them?

Adjustable factors to make the interest rate cheaper would be, on the one hand, the term and on the other, the availability period. 20 years is already very long and certainly cheaper. And 18 months availability period is above the standard of 12 months, which also costs.
It might also make sense to take the KfW loan variant. However, the 10-year fixed interest period is likely to conflict with your desire for 30 years of security.

The monthly lease amount would be 250€.

The problem is that the contractor only classifies us for 3.2022 if we wait until July because of [Kfw]. Then 6 months construction time makes about October 2022. The usual 12 months provision would be too short.

But then you wouldn’t need a loan now, right? We only took it out shortly before the start of construction, so hopefully the 12 months will be enough.

And 6 months construction time? Prefabricated house? Our requested general contractors have stated 10 to 12 months as construction time, and the prefabricated houses were also contractually guaranteed only 10 months.

How you can come to 420k construction costs with a granny flat is a mystery to me. We are above that even without a granny flat.