@al17online 

1. I would opt to have the Deco take the place of your existing router, and keep the Sagecom as a backup incase anything happens.

Pretty much what you mentioned about using AP in that a majority of the router features will not be available. If you want to keep your existing router, you can make the Deco an AP, but it would be recommended to disable the Wi-Fi on your router and let the Deco handle the wireless aspect.

2. The switch would go after the Deco that is wired to the modem.

3. Only the Decos themselves will be the mesh network so you can configure the Deco to have the same name and password of your existing network. When you set up the Deco for the first time you will put what you want the network name to be and password. If you keep your original router up having the wireless network on that enabled will cause issues, both with interference and drops from clients jumping back in forth.

4. Yes, once they are set up you would unplug them, and place them were you want to be. The device will power up and automatically connect.

5. That would work. Any Deco unit can be treated as if it was the router where you can attached wired devices or switches.

6. You are right about the fast roaming, that would be a feature to disable. As far as the guest network, you will be able to create one, and disable the 2.4GHz in AP mode.

One last note is that you can mix backhauls so you can have: modem <---wired (must be)---> Deco <---wired---> switch <---wired---> Deco 2 <--- wireless ---> Deco 3

Here is also a FAQ we have regarding Ethernet backhaul: https://www.tp-link.com/us/support/faq/1794/

Thanks for the reply Tony.

So, you dont really see any benefits on keeping the router (wireless function off)  to the Deco? My concern is that I all the ports to the device plugged into hardware and have IP's for those devices.

This is the plan... make sense? You see any problems?

Basement (cable drop) -

modem  ----> router (possibly)  ---> deco---> switch (1)   

   from that switch (1)---> cat 5 to a 2nd switch (2) ----> to smart tv and to a Streaming device  (NVIDIA Shield)

also from switch 1 (basement)  ---->wired to 2nd floor

1st floor

Deco  (wireless)---->wired (cat5) to smart TV

2nd floor

Wired Deco (from basement switch 1) ---> wired (cat5) to  switch (3) with a cat5 to PC

@al17online 

If you have existing configurations on your current router then it probably would be best to go with AP mode. That would give you the mesh coverage without having to do additional configurations with the Deco being the new main router.

Topology looks good.

Just as a side note, when setting up the Deco units initially it will be in router mode, but once you are all done go back in the Deco app and switch to AP mode.