I wouldn't worry about how good your friend is, we have teams of all ability levels entered. While there are squishes like me, there are also teams with several hundred wins per player. The group phases will likely be a glorious nightmare, but the elimination phase will be showcasing the top eight teams in the event, so -whatever you do - don't let him leave!
As for German language casting, this something that I'm really interested in doing actually. If we have enough casters who can/want to cast in German then I'll set up an Absolute Bedlam DE channel on twitch. Primarily, casting should be english (for maximum accessibility, but If there is another caster already, then Offering German casting would be great!