3. Do you need to enable the media library and scan all shared folders - what is the advantage?
No, you don't have to. If you wantaccess to your media files via virtual folder in XMB you have to enable it. It offers additional features like music sorted by album, artist, genre and so on.
4. All the video web services come up black - what can I do to fix that?
I depends... There are bugs in later versions of VLC, also lots of sites which offer content try to sabotage third party applications to use their media. Also this web streaming thing is not main focus of the developers.