Let's start by telling what device exactly you have there. :)

Powerline adapters don't have IP addresses. If this is a Powerline/WLAN AP combo device, unhook it from the router's network, do a factory reset on it, and hook it directly to a PC's LAN port for...

Well ... this latest firmware still uses Qualcomm core firmware 2.0.0-5. Other major manufacturers have updated to 2.2.1 recently. Here's hoping that TP-Link will follow suit shortly.

Another new firmware has been released, apparently enabling IPTV streaming optimizations. EU version here: http://www.tp-link.com/res/down/soft/TL-PA8030P(EU)_V1_160328.zip UK version also available,...

There is nothing Linux specific about using the web interface. Just open your browser of choice and follow the instructions in the manual.

Doesn't matter, for Powerline is entirely point-to-point, all connected devices are treated the same.