Thanks Krenek, but that didn't work for me.

• I had already a Google+ account and used that account and mail address for my first login in the new GEC.
• I guess that I have to live with the anonymous avatar because I do not want a full link to that Google profile.
• For the e-mail: Look at the top of the Open Forum and click on the "My membership" button.
  You have e-mail options there.
  

Most important is that they find a solution to link our old and new posts together.