macOS High Sierra Installation Fail
David Anderson was right. The Disk Maker X was the problem. The bootstick was corrupted apparently.

I created a boot Stick via Terminal

sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume


The last time I did this a Bootable Stick wasn't as easy as one terminal command that's why I used this 3d party tool. Better keep away.

Thanks for the hint.