I looked at your post because I just happen to speak German. I noticed your post is in English which leads me to believe its no problem for you.
While I can't answer your question I would make one recommendation. Post your titles in English also. This will help you get answers not just from those in an English speaking country but internationally also. I totaly expected your post to be in German. If I only spoke English or English/and some other language I would never have looked at your post.
Here is what I think I can help you with.
1. Do i have the possibility to change the bullet points in the lists in a square?
(assuming you are talking about the template). If you delete them and start over they will auto generate. For example if you number them 1.2.3 etc... every time you return to a new line a new bullet will be created.
2. Can i remove the video-backgroundframe or change the frame colour/design?
Not sure on this one. I have not tried it. You could possible if your using iMovie or iDVD to create the clip. The background color can be changed through the color settings.
3. Is it possible to show a video in fullscreen mode?
Sorry have not tried this one.