Compare construction financing offers - Which one is realistic?

Maybe you can't have everything at once ... ?

400k and 115k of that for the land. What kind of house do you intend to build with that?
Switch to saving mode and take another look in three years.

Difficult. Such long commutes. A lot of money goes on gas and the car because of that

Could one or both perhaps switch to commuting by train? This is usually significantly cheaper with season tickets and with a proper connection is no more annoying than commuting by car. Additionally, it is healthier.

and look again in three years.

That's exactly what we will not do; the construction is expected to be applied for in spring 2019.

Can one or both perhaps switch to commuting by train?

The problem will then be resolved with the house construction; combined, both will then drive a total of 40 km per day instead of 200 km.

We will build about 150m² of living space, but that is a topic that will not help the OP.

If you have an offer and can live with the conditions, why wait unnecessarily and keep saving? That doesn't really make sense. From my point of view, the gained free time (due to shorter distances) is invaluable. We notice it ourselves. My husband now takes only 30 minutes instead of 45 minutes to get to work, and I can get there by bike in 3 minutes. The reduced burden is worth a higher loan to me (I also save a lot on fuel).