Yes, sometimes it might help to have multiple providers on different backbones if you run into availability issues.
There are currently no legal cases in Germany against Usenet like with copyrighted material and torrenting, that's mostly because you don't distribute with Usenet.
Yes, so it would if it gets posted to any community you follow yourself. This is an absolute cluster fuck and not worth it if you are not prepared to deal with moderating illegal stuff even on your one user instance. Some people are just way too naive and ignorant of the laws around stuff like this. In Europe your are way more at risk as a platform/website provider/hoster than you are in the US and this can bite you in the ass really hard if you are unlucky.