Hello Martin and welcome to the Wowza support forum.
You are correct, mp3 is not supported on Android:
Most Android devices support RTSP/RTP streaming. When streaming to an Android device using RTSP/RTP, the RTP portion must flow over UDP. Android doesn't support RTSP/RTP interleaved (RTP over TCP). This means that if UDP is unavailable for RTP playback, RTP over TCP won't work as a failover and your stream won't play. Android devices can't play MP3 streams over RTSP/RTP in any combination (audio/video or audio-only).
Hi, please take a look at this guide on setting up the Transcoder. If you have any specific problems along the way let us now, preferably in a new thread. And we will see about helping solve them as they arise: