thanks guys,

For Q2, I have done my research, and found out somebody else had the exact same problem too. And his finding was the incompatibility between his router and n900. I strongly believe this is also my case. My router is Billion 7404VOPX. Will buy another router and try.

For Q5: battery performance improved with a few charges. Also found out, after fully charging, if you don’t disconnect your charger, you actually lose power slowly, if you turn on you phone immediately after you unplug your charger, you lose large amount of power, so give a few mins to cool down.