@MatanR 

Archer VR600 home router is not compatible with Deco mesh. Archer VR600 router WiFi coverage can be extended by adding OneMesh range extenders.

It is possible to run Deco mesh together with Archer VR600, but Deco mesh will run its own WiFi network. If you plan to keep Deco M5 set anyway, I can give you more details on how to achieve that. 

  @Alexandre. Thanks!

So with you input I am disconnecting the Archer for the Wifi network and keeping it as a modem only. 

is it possible to have 3 Deco M5 connected to the switch (if too far from one another)? 

  @MatanR 

Turn off WiFi on Archer router, don't make any other configuration changes in it.

Add and configure Main Deco through Deco app. Main Deco must be wired and I would recommend for initial configuration to connect it directly to Archer router with short Ethernet cable.

Change Deco Operation mode to Access Point: How to set up Deco to work in Access Point mode

Add Satellite Deco to Deco mesh, but do not have them Ethernet wired (yet). Bring them to where Main Deco is, so that they have good WiFi link to it, and add them through Deco app.

After they are successfully added to Deco mesh, take Main Deco and Satellite Decos to their permanent place and wire them there. As long as networking switch is compatible with Deco Ethernet backhaul, you shouldn't have issues. More of that topic here: General questions about Ethernet Backhaul feature on your Deco