I want to support only one Beacon standard if possible, and have the device itself act is the "host/beacon", and other devices the "listener".
I'm supporting Android, iOS, and possibly Windows phone using Xamarin.
Is any interoperability supported between iOS and android?
Check this library to give you some guidance.
https://github.com/AltBeacon/android-beacon-library
It allows Android devices to use beacons much like iOS devices do. An app can request to get notifications when one or more beacons appear or disappear. An app can also request to get a ranging update from one or more beacons at a frequency of approximately 1Hz.
You can also find more information on this blog: http://vincenth.net/blog/archive/2014/04/24/building-cross-platform-ibeacon-apps-for-ios-android-and-windows-with-c-and-xamarin.aspx