Hello @desperardo 

Sorry for the late reply, I hope I could help, please check my answers below:

1.  Powerline KIT have to use under the same electrical circuit, that means under the same power meter 

You may also check FAQ here for more details:  Q3.10: Can Powerline adapters work if they are separated by Circuit Breakers/ Fuse Boxes/ Fuse Boards?

Most frequently asked questions about TP-Link powerline devices

2. we do not usually use direct distance between the 2 locations, but the house powerline distance, usually powerline kit could be paired under the same powerline in the same house (within 300m powerline distance )However, with noise, interference, and line quality the range the powerline adapter can reach may be reduced.

3. TL-WPA4220 could work with BT router or routers of different manufactures

4.  If PC connected to router and camera connected to PLC extender , or vice versa, PC and camera will be the under the local network, as all the IP address are assigned by router.  For camera streaming question, you may consult CCTV camera support for more details. 

Hope the above helps.