As I know, when you restart the router and plug the USB driver to another USB port, it will re-scan. You may give a try. Obviously, it is not quite convenient but not sure if they will add the...

Firmware Version? Are you using the same SSID and password for powerline extender and main router? Since the ipad mini works OK all the time, the extender should work OK. Try to change channel on web...

Not sure as it is not in the compatiblity list of W8968. You are a reseller? You may test for the customer and his dongle? :)

Your MR3040 is V1 or V2? If it is V2, maybe you can try to get a beta firmware from TP-LINK support team and test if it works. http://ticket.tp-link.com/index.php?/Tickets/Submit

Do your mean powerline light is off? You got two? PA4010 and WPA4220? Run the utility for PA4010 and reset both of them. After reset, check if powerline light will be on. Or try to set the same...

MR3020 works in 3G/4G router mode? Internet access is 3G/4G Only? Are you connecting a PC to its LAN port? Check status of local area connection on your PC. Any IP address, default gateway etc....