@AshTheDash 

Can you update your original post with the TP-Link terminology, such as:

ISP modem/router (provided by your ISP)

Main Deco

Satellite Deco

That would make it much easier to understand. For example, when you say "how to connect all 5 routers to HUB" I can figure that under "Routers" you mean "Deco," but what is "HUB?" 

Also, "how to connect 5 Satellite Deco to..." and "how to connect Main Deco and 4 Satellite Deco to..." may get you different answer. 

Take a look at the following FAQ and terminology it uses: General questions about Ethernet Backhaul feature on your Deco

Parts that I understand from your questions I can answer now:

1. LAN cable connection will work. LAN is actually preferred, hardwire as many Satellite Deco as you can for best WiFi coverage.

2. Deco units have gigabit Ethernet ports. Wired Deco unit can deliver up to 600Mbps over WiFi. Having them wired will not decrease the speed of 200Mbps Fiber link. In the future, you can up your Fiber link to 500Mbps if you have that option from your ISP, and M9 Plus will be just fine with that.

It is my home network setup, actually: M9 Plus with 500Mbps Internet link.

3. I don't know what is "HUB," but you might need to buy swtich. It must support Ethernet backhaul protocol used by Deco mesh. Unmanaged gigabit 5- or 8-port TP-Link switch is what you should get.

4. I don't know what "Hub Router" is and how it is different from the "HUB."

5. Maybe, but it depends on what is "Hub" and it may require to configure Deco mesh to run in Access Point mode. See Switching a Deco to Access Point (AP) Mode

Hi  @Alexandre. 

I edited my original post as suggested by you.  Thank you for the pointers.

Also appreciate your reply on some of the questiona.

Can you revisit my post and see the edited version and help me with my other questions?

Can the Deco M9 Satellite deco units connect with each other even if they don't have line of sight?

I can have CAT6 cables laid to all the rooms and have all the Satellite Deco units connect to the Main Deco through an unmanaged switch. Will that help me improve the connectivity and download speeds?

Will upgrading to XE75 will help improve with the connection? Ofcourse there are other benefits of the upgrade as well?

  @AshTheDash 

"Can the Deco M9 Satellite deco units connect with each other even if they don't have line of sight?"

Yes, they can, but it is not guaranteed. You have to try it at your place, because type of materials used for walls/ceilings between deco units will impact quality of Deco connections. Also, even in an ideal scenario, expect speed loss of about 30% on devices connected to Satellite Deco using wireless backhaul. More if Satellite Deco units have weak connection between each other.

"I can have CAT6 cables laid to all the rooms and have all the Satellite Deco units connect to the Main Deco through an unmanaged switch. Will that help me improve the connectivity and download speeds?"

Yes, it will. Each Satellite Deco with Ethernet backhaul will deliver same speed as Main Deco, and with Internet speed of 200Mbps that means 200Mbps WiFi speed.

"Will upgrading to XE75 will help improve with the connection?"

It will not, as long as your Fiber speed is under 500Mbps. Deco M9 Plus will do as well as XE75 on Internet speeds under 500-600Mbps.

Thank you for your response and appreciate you answering my questions.

What should be the specs of the un managed switch o be used for the 200/300 Mbps connection, to help create the mesh with 1 Main and3/4 satellte Decos

Wil this work?

8-Port 10/100/1000Mbps Gigabit Ethernet Switch | Reliable Switching Performance| RJ45 Connector | Switch Capacity: 16 Gbps | Plug & Play

  @AshTheDash 

For 8 ports, TP-Link recommends the following switch: https://www.tp-link.com/en/home-networking/soho-switch/tl-sg108/

In general, look for TP-Link brand of gigabit unmanaged switch, 5- or 8-ports. Other brands may work with Deco mesh, too, but it is hit and miss. 

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Also, you can connect Satellite Deco by Ethernet cable directly to another Satellite Deco (daisy chain). You can have some of Satellite Decos connected to the switch and rest of Satellite Decos connected to them. 

  @Alexandre.

Thank you for the response..

Ash