@nyonyo 

Start with this document: General questions about Ethernet Backhaul feature on your Deco

  @Alexandre. 

"When the Deco is set to work under Access Point mode, you can wire satellite Deco to any Deco unit or the main modem/router".

Simply put, does this mean all Decos can be wired directly to the modem/router in Access point mode, but there has to be a main Deco and satellites in router mode?

  @nyonyo 

All Deco nodes can be wired to ISP router, when Deco mesh runs in Access Point mode.

Main Deco must be wired to ISP modem/router. In Access Point mode Main Deco can be wired to home network, not necessarily directly to ISP router, but it still must be wired.

You can't wirelessly connect Satellite Deco to ISP router. Satellite Deco must connect to Main Deco or to another Satellite Deco. 

In Access Point mode, Main Deco differs very little from Satellite Deco. If Satellite Deco is connected to the ISP router, its traffic will go directly to ISP router, not through Main Deco.

In Access Point mode, with multiple Deco nodes wired to your home network, you can even power off Main Deco and Deco mesh will keep running: https://community.tp-link.com/en/home/forum/topic/583064

  @Alexandre. In terms of wiring decos, do we have to do it purely with Ethernet cables or it can be done through powerlines too? My modem/router has many ethernet ports, do I still have to use a switch to wire the decos?

  @nyonyo 

If we are talking about Deco Access point mode, you can wire Deco node to any available Ethernet port you have in your home network.

In my house, for example, Main Deco is connected to switch which is connected to the ISP router. One Satellite Deco wired directly to the ISP router. Another Satellite Deco wired to the switch which connects to a different switch which is wired to the ISP router. Third Satellite Deco connects to Main Deco wirelessly.

You can use all Ethernet ports of your ISP router.

You can use powerline adapters to wire Deco, too. You should not expect fast speeds when using powerline adapters, also not every brand of powerline adapters is compatible with Deco. I would recommend powerline adapters with single Ethernet port on each, because for some reason those with multiple Ethernet ports per adapter have more chance to be incompatible with Deco.

TP-Link brand of powerline adapter should be a safe bet, but I also tested with ZyXel and it worked for me. When Deco node establishes backhaul link through powerline adapter, it'll report that link as an Ethernet link:

I would not recommend connecting Main Deco through powerline adapters, but there are people who are doing it.