I reached a point, I don't get further without some hints from you guys. Please.
My aim is scribbled in the following image. I got it done up to the dashed line.
Here the link to the Edge Animate File (zipped package) with my status quo: http://intern.ixtract.de:80/_AI9YCz3iBfbM6R
I would be happy, if I could get some help.