Thanks Jake Lo,
finally i was able to boot from the stick and as a next step i did install macOS on my SSD drive without any problems.
nonetheless I'd really like to know / understand what the problem was / how it works.
further more, where can i find the guide for the next steps, in order tohave all drivers installed (especially for my WiFi Card),
booting to macOS without the USB stick
giving the mac the chance to come back from (sleep / black screen).. it freezes when the screen turns off.. or is it because of the hard drive that turns off after a couple of minutes?