Couldn't I just pay all of that stuff by my own to show them I have no intention to do so? I want everything to be legal. I do not want to save any money in taxes, health insurance or social insurance. I am actually happy to pay all this. Nevertheless I heard horror stories even by doing so you are at risk they will f..k you anyway after a Prüfung (audit) within the first five years or so.

Don't take my advice for figuring out a real-life situation.

Wouldn't you actually be paying more taxes as a one person company? Why does it matter if the company has only one client and one employee if everything is paid properly?

It's about the public tax fund.

You have to pay into it of you're employed and make below ~4800€ (before taxes) a month.

It's rather much % of your income, so you can save rather much by not paying it.

-tax +pension sorry

Because as managing director you don’t have to pay pension insurance (and others). So if you are employed, the social system will get more contributions.