... which is exactly my point. V1 firmware hasn't been updated for ages, still running on the original (and not very good) Qualcomm core 2.0.0. V2 is on 2.2.3 currently, while Qualcomm themselves...

I always configure new hardware on an isolated machine before deploying them into the live network - even at home.

My favorite approach - if the router supports it - is to deploy the switches in DHCP-client mode, and assign them a static IP in the router's DHCP server. That way, IP address configuration is kept...

What's the physical bandwidth on the PLC line (as shown by the tpPLC utility)? Also, if these are 8030P V1, early firmware did show rather miserable throughput. Try an update - or, if you still can,...

You could - in theory - erect two separate powerline networks, each with its own PLC adapter in that intermediate building, and bridge the two with a LAN cable.

These aren't available from TP-Link. Best advice is to return the plain kit you have, and buy a WiFi kit plus a single plain adapter - those are available in single pack.