AirPlay Questions

Hello, I have an old Intel iMac running OSX 10.6.8 & iTunes 11.0.1 & I'm wondering if I can use Airtunes on this set up to run a multiroom music system. I'm thinking of an AppleTV unit connected to a 5.1 surround sound system, an Airport express connected to an existing stereo unit & maybe 1 or 2 dedicated airtunes docks for bedrooms etc.

If my hardware/software is up to the job, the other possible problem is that we do not currently have an apple hand held device (iPhone, iPad, ipod Touch etc) to use as the controller & I don't want to control the system from my desktop. We do have several Android mobile phones & an Android Tablet (Nexus 7) in the house - Is there an app etc that I could use to enable one or more of our Android devices to act as the controller for the system?

If all this is possible, the other question I had was would my iMac have to be on & iTunes open for Airplay to work, or would it work even if the iMac was not logged on (sleep mode etc)?

Thanks for any advise!