Hi,
1. By default, our header has a margin bottom and if you want to remove it on your home page, you can simply add a negative margin top for the first row on the page with Visual Composer. So just set -40px for example to compensate it.
2. You can disable it in Theme Settings -> Social profiles.
3. You should be able to find it in Dashboard -> Dummy content (left menu). It may be disabled in Theme Settings -> Other.
4. Sorry, but there is no option to change the width of the container in our theme.
Kind Regards