Single-family house 1,000,000 affordability - monthly installment?

Well, just wait and see about the shortage of skilled workers. It’s not getting better and we are talking about in 20 years. Many a door will probably still open.

If the equity is 650k cash or liquid (stocks etc) so what?

Build

Yes, as long as you don't spend the money on sports cars, stock gambling (Wirecard and co) or similar and lose it, everything is super safe. It just yields more returns than the loan interest costs. With sums like that, it's at least worth it.

Oh, and even if the money is gone, the income is more than enough to service the loan. Very comfortable situation.

Honestly, after the StEx, I simply lacked the points for the public service (lawyers know the drama). I was unfortunately forced to try my luck elsewhere... Everything has its pros and cons

Then, given your salary, it seems the big law firms have really lowered their requirements quite a bit :D No, seriously, if I could, I would do exactly the same: leave out equity and invest elsewhere. Or rather, I would definitely treat myself to KNX first.

With conventional electrical work, 50,000 euros should be more than enough,

No, with conventional electrical work you can equip at least two houses with that amount, rather three. For KNX, however, depending on the requirements, it will be a bit tight, and then your mentioned surcharges apply.

Did I read that correctly that a property with a seven-figure value is being contributed to the project? This is not included in the 650k equity? Dude, then just go for it and don’t think twice :)