I am looking to expand my network, as the range is a bit to low for all my Tapo cameras and plugs. 

I currently have a Archer C80 in AP mode to distribute Wifi in one end of my house.

And an Archer A5 AC1200 in AP mode in my office, currently distributing Wifi with another SSID than the first one, and also as a switch for my computer.

However as the A5 does not have gigabit switching, and restrains my speed to 100 Mbit's, i am looking to replace it for a switch or router with gigabit ports.

Both routers is connected with ethernet cable to the same router from my ISP that is placed right next to my C80

I as wondering, is it better to get another C80, and is it possible to mesh both C80's in AP mode, connected via ethernet cable?

Does the first C80 need to be set up in router mode? And how to avoid IP conflicts, as my ISP router is currently distributing IP addresses.

Or is it better to install a simple gigabit switch in the office, and replace the A5 with a range extender/AP with ethernet connected