Well, "a good stash" is a good way to put it. Some of the available equity will also be directly deducted for the kitchen to be purchased. A liquidity reserve of at least 5,000 euros per person should also still be available. That leaves not too much "in the stash" that could really still be contributed to the house construction if necessary. If something unforeseen comes up, it means immediate additional financing.
With your income, a new build is definitely possible, but certainly not on this scale. Either the plot must be significantly cheaper or smaller, or the house to be built on it. You have to be that honest with yourself, but that's also normal. You certainly wouldn't be the first for whom the castle turns into a small castle.
Here is an example I got today from the financial advisor (who inquired at several banks).
1st bank: 100% financing; 15 years fixed interest period; effective interest rate: 2.1%. Did not accept our plot as equity because the plot is financed through them. And they do not agree with the increase in the standard land value. Is our house bank. But I will still talk to them.
2nd bank: under 80% financing; 20 years fixed interest period; effective interest rate: 1.21%. Accepted the plot with the current standard land value.
The approximately 1% interest difference is already enormous.
That was the first offer. I will of course still go to at least 3 more financial advisors. I think it will be similar for you with 100% financing. If you want to finance over 100% (additional purchase costs), then it will be even more expensive.