Live Streaming solution - HD streaming hardware and software

Hi guys, I have a question for you:
a client asked me if we could make a live streaming with 2-3 HD cameras for e-learning lessons, and if is possible to give to the students the ability to asking questions to him with an audio connection.
i've read a lot of posts on this forum and other, and my conclusion for live streaming is that we need:
- a switcher, like ATEM 1 M/E from blackmagic
- an h.264 encoder, like matrox mojito or blackmagic h.264 recorder
- software for live streaming like wirecast
- server for streaming like ustream, livestream etc...

But i have a lot of doubts about it:
- is that the better way for streaming HD videos live on the net?
- i've read that both matrox HW and h.264 blackmagic have problem, is that true? there's another HW configuration that i'm not considered?
- after i've created connection and streaming from the teacher to the sudents, how can I set-up an audio connection simply and fast from the student to the teacher?

Thank you for your help, if you need other information just ask me!

Thank you for your advice! If I choose blackmagic ATEM what kind of I/O box i should buy for working with wirecast?