Which firmware did try to upgrade? With firmware upgrade failure, you cannot login its web interface anymore? Only some TP-LINK products have firmware recovery feature, yours excluded... I'm afraid...

Sounds like a DLNA compatibility issue as the Samsung Galaxy S3 works but Samsung ES6700 doesn't work.

WAP2 is the security type instead of Wi-Fi password. No worries.

Go to Online Clients page and you can block some of them. Blocked clients will show up on Black List.

I didn't find any TP-LINK 3G/4G router has a gigabit port. Your PC's Ethernet port is gigabit? http://www.tp-link.com/en/products/list-4691.html

You got a PA4010 to work with WPA4220, right? Provide the detailed topology.