Construction financing over 700k - Is the offer okay?

You would quickly be at €406,000, and additional construction costs (15%?) and kitchen are still to come.

No, kitchen and additional construction costs are included in the €100,000.
Purely for the house with basement €500,000! How do you get 145 sqm? That is nowhere stated. And since no further information about the size is given, I assume I am not entirely wrong with 160 sqm plus basement. If it is not even planned to be bigger.
Only apparently no OP here wants to hear that they should part with 30 sqm or their stock portfolio to have a more relaxed life, because a negative concession immediately follows.

Thank you for the partly really constructive suggestions! The idea, of course, is to push the total amount a bit lower and finance even more through equity and/or partially liquidate the [Depot], the only problem is the double burden until the house is handed over, as the house will not be ready to move in for another 26 months and consequently additional commitment interest will be payable, for which we want to have sufficient reserves. The costs of the earthworks are also difficult to calculate in advance. I know there are providers who build faster (and cheaper), but we have put a lot of care into comparing the house providers and are now more than satisfied with the quality and service. By the way, it is not 160 sqm, but a little more than 140. We do not want to make compromises in size or house quality because we would rather pay off a house designed entirely according to our needs for a longer time than pay off a poor compromise for a shorter period.

Basically: Whether it can be sensibly represented or not must take place well before the purchase of the property and planning/house offer request (cost breakdown)!

With whom or what was this discussed? Has the house bank basically given the green light?

Die 700.000 sind alles tutto completti

Auch die Kosten der Erdarbeiten sind im Vorhinein schwer kalkulierbar.

Hm, is the house price at least fixed at 500k€?

Problem ist nur die Doppelbelastung bis Hausstellung, da das Haus erst in 26 Monaten bezugsfertig

The home builder has already clearly indicated that we cannot start before mid-2022?! Or how does this timeline come about?
Is the house even fully planned yet?

Honestly, I don't quite understand where the problem lies.

At least 7,400 EUR p.m. net will be available in the foreseeable future; minus health insurance then still 6,000 EUR p.m. For bridging until then, there is still a significant liquidity reserve. In addition, the jobs are crisis-proof and one is doubly protected from dismissal.

The external capital requirement can be reduced by 50,000 EUR through personal contribution (teachers should have enough time for this) and subsidies. Possibly a few extras and/or fewer square meters and it can be reduced by another 50,000 EUR.

In my opinion, with 600,000 EUR or 650,000 EUR external capital requirement is quite manageable - without knowing the private spending behavior.

To the actual question:
Interest rates are standard conditions for BA > 100 %. Possibly there is an offer via a direct bank with 0.10 % less. However, a financing commitment from a direct bank is difficult to represent given the current situation.

The problem is just the double burden until the house is handed over, since the house will only be ready to move in 26 months from now and therefore additional interest on the loan commitment will be due, for which we want to have sufficient reserves.

These should always be taken into account in the total cost calculation and financed accordingly.

My personal freedom always begins with my financial freedom. I would not let myself be a slave to my bank or my employer for 30 or 40 years. Respectively, I have oriented myself exactly that way. House purchase and house construction managed without a loan. Today we are very glad about that. A few hard years, certainly.