let me give you 2 links that will cover your basic questions. The texts are in German, so please use a translaton service like Google translate.
1. Non commercial broadacsting in Germany: https://de.wikipedia.org/wiki/Nichtkommerzieller_Rundfunk
2. Founding a webradio: What you should know: ****://***.helpster.de/radiosender-gruenden-so-geht-s-im-internet_71341
Finally a good starting point in German, made by young radio professionals: https://***.radio-machen.de
All the best and a happy new year!