If your receiver is connected to the WiFi then it should work, but as part of the whole system. So, you might only hear it as a "left high", "Right Surround", etc... Not sure, but I bet there is a system/software out similar to Sonos that would give you the "sound through the house" effect I believe you're looking for.
I doubt it - though you don't say how you connect to your receiver. Generally an iOS device can only play to one Airplay device at a time, or though the dock connector/ iTunes can play to multiple Airplay speakers and if your receiver is on the WiFi this could give you music from your main PC / Mac through your receiver and through the Klipsch at the same time. But I don't believe this can be done with music playing fro your iOS device itself.
I don't believe so. The G-17 is an airplay device and when AirPlay is in use the other outputs (earbud jack) is disabled and if your receiver is AirPlay I believe that your iPod will only sync with one device.