You can stream from several cameras at the same time, just follow this guide for each source.
You can stream video+audio from one or more IP cameras, and you can stream from shoutcast at the same time using the same application; in the StreamManager step use MediaCaster type "rtp" to start the camera, and use MediaCaster type "shoutcast" to start the shoutcast stream.
Wirecast should send h.264 video and AAC audio. I think the Sam Broadcaster is shoutcast server, which is audio only. Both are supported in Wowza. I don't know of any way to enforce any kind of synchronization.