General questions on Airport Express & audio streaming

I intend to buy the new Airport Express. Scope is to extend the wifi coverage at home and to stream music to my audio hifi device. I already have a Technicolor DSL modem (with wifi) providing my Internet services and I intend to connect the AE with an ethernet connection or through wireless bridging.

Q1: Can someone confirm my assumptio that the AE can be used to extend the wifi coverage at home?

Q2: Can I still stream music through the AE irrespective of whether my laptop is connected to the AE directly or further more through the other (non Apple) wifi router at home?

Q3: is iTunes the only strreaming client supported by AE?

Q4: Can I stream iTunes through an Android mobil device? Or can this only be done through an iphone?