When the Nanostation is set to Bridge mode, PPPoE is selected as WAN connection type on web interface of WR940N? WAN IP address obtained is a public one then? If it does, try port forwarding or DMZ....

WR740N will be the main router and WA850RE will be the range extender to extend Wi-Fi range of WR740N? If so, first, you have to configure WR740 and make it work with your modem....

Did you update the latest driver of T2U for Windows 8.1? http://www.tp-link.com/en/download/Archer-T2U_V1.html#Driver

After reset, did you pair PA4010 and WPA4220? How about status of powerline light? http://www.tp-link.com/en/faq-258.html Can you connect your computer to LAN port of WPA4220 and check if it can be...

It has been answered here. http://forum.tp-link.com/showthread.php?81557-Lenght-of-time-to-charge-unit&p=163105&viewfull=1#post163105

There is no TP-LINK driver for Windows 10 but it is verified that the driver for Windows 8.1 can work in Windows 10 without a problem. So you can purchase it...