I don't think WR841HP is powerful enough to cover 120M square. Is it a multi-storey house or not? You may need a range extender or some powerline devices.

How do you know the command? If you have a very noisy line, I think you should contact your ISP to solve it.

If SNR Margin is lower than 10dB or Line Attenuation higher than 45dB, your line quality is poor and may suffer from Internet dropping. In this condition, you should contact your ISP to check your...

What kinds of devices? Report the problem here directly. http://ticket.tp-link.com/index.php?/Tickets/Submit

Where did you see that? System log? Provide a screenshot if possible. Besides, if no problem with your internet connection, no need to worry about the log.

Read this. http://forum.tp-link.com/showthread.php?76213-WPA4220-seems-to-block-dhcp-trafic&p=159449&viewfull=1#post159449 By the way, did you submit a ticket to report the problem? Not sure if there...