No. The frequencies used in wireless communications are nothing near to the frequencies that would damage your health.

Answer:
There’s loads of debate about the safety of wireless and WiFi, but seriously, i wouldn't worry about it. I sit and sleep by my wireless router and it hasn't affected me. Also, a normal Wifi card/adapter gives out about 0.4% energy of what a mobile phone would.
Answer:
None at all, its completly safe, i dont use it though because an ethernet cable it more reliable than wireless.
Answer:
No. None whatsoever.