OK, I have been trying to setup ethernet backhaul and failing miserably - I am guessing it's either me or my switch.

First off, this is all set up in the basement of my 3 floor home (basement, 1st floor, 2nd floor) in the furnace room which has the electrical box, the furnace, water heater, huge metal ducts such. This is probably the shi**iest place to have it as there is mega interference and why Wifi sucks and I resorted to a mesh system. 

Here is my set up in words:  

- I have Centurylink 1GB fiber coming into the house and into the ISP provided modem - Wireless radios turned off

- I have a 16 port Netgear unmanaged POE switch connected to the ISP provided modem out of Port 1.  The 16 port switch has ethernet cables running from it from a legrand wallbox with 2 8-Port Cat 5e Network Interface Modules to which then supply to all the rooms 

Deco Setup:

- I have the basment (main) deco X60 connected to the ISP Provided modem out of Port 2

- I have the 1st and 2nd floor Deco X60s of the house working wirelessly but they lose connection off and on. I have tried to move em all around etc and and twhile hey can be connected via ethernet wire in certain spots, they are not right now as I am failing at ethernet backhaul!

I tried 2 methods:

- Connected basement deco X60 connected via cat5e to the 16 port switch and the other 2 decos in the different rooms also wired into the switch and had one cable running from the ISP modem to switch. This did not work.

- Connected basement deco to ISP modem via cat 52. Left the 1st and 2 floor decos into the 16 port switch and ran a line from the switch to the 2nd ethernet port on the main deco in the basment in hopes to get wired backhaul. FAIL. It made several of the other ethernet ports in the house stop working somehow. 

So, right now - I have the basement main deco x60 wired into modem lan 1 port and the other 2 connected wirelessly to it. 

I read that if I get a d-link or some other switch, IP conflicts can happen, so I want to buy a dedicated 4 port switch for the Deco X60, guessing managed and plan to run all 3 Decos into the switch and one from switch to the modem. This way I keep the deco network separate from the wired network.  

Will that work? What switch should I buy? 

Sorry for the verbose post. Hoping to explain myself. Thanks for reading and appreciate any responses!