Design done ...for the moment
Three days later the website looks like something. What I did not expect was that the first thing I had to to on Blogger was to dig into the html of the template to make it work.
The worst mistake was that every background picture I tried (regardless of the size) was tiled in the header section that stretches completely over the screen. Looking into the forums I found that I wasn't the only one who had this problem. (I posted my little solution.)
I am not the big CSS guy - maybe because most of the times other people stack the boxes and elements in a different way I would do it and I really hate it to fix that rubbish - but a little search, try and error brought the solution. So it's not a great design, but it does not look like a standard blogger template anymore. Ready to go now.