What are you trying to block? Describe in details pls.

I'm afraid not. Why not update your MAC OS? Or you can login its web interface using the method as below. http://www.tp-link.com/en/faq-464.html

No problem with your understanding. Most people prefer to use same SSID and password as the main router.

I consulted TP-LINK support team on firmware issue and got a reply as below. The firmware of powerline adatpers like PA6030 is composed of PIB and NVM. A new firmware released may not upgrade PIB and...

A piece of advice for you. Pair your powerline adapters or set the same unique network name for them. There is an instruction. http://www.tp-link.com/en/faq-258.html

Did you download the web plugin here? NC200 is connected to the router by cable connection or wirelessly? What's the version of your IE? https://www.tplinkcloud.com/download.php