Like so many, you are confusing physical line speed with payload throughput. The former is gross bandwidth, the latter is net throughput. As with WiFi, net throughput is never more than 1/3 to 1/2 of...

The web interface of the WPA should let you do this.

Did you use proper procedure to make them all part of the same powerline network?

My personal experience is that after you used the Config Tool once to enable either DHCP client or fixed IP address, access through web browser becomes reliable. Only this once for initial deployment...

It's not so much about the router, much more about any extra switches and WLAN access points. Those need to be multicast-aware as well, or else your IPTV traffic will multiply onto everything, not...

Start over - trigger a "factory reset" on all devices involved and then try again. Please consult the respective manuals on how to do this.