@daBowmore 

I would probably go with the Deco M5. 

Regarding your layout, what you would do is connect the primary Deco, then add the other Deco units in the same room (just plug the power). Once all the Deco units are added, switch the operation mode to Access Point. 

The reason why you need to run as an Access Point is that you have all connections leading back to your router and only AP mode will allow that. A drawback is that most of the Deco features will not be available. Putting the Deco in AP Mode will allow you to have all the Decos connecting to your router. If the Deco is in router mode all the slave Deco units must connect to the main Deco (main Deco in front of the switch).

@Tony Thanks!

I am happy to hear that this layout would in principle work. Already place the order, but I went for M9 as I got a good price for it.

But I got bit concerned since you mentinoed the missing Deco features when using Access Point, and I found the following:

• DDNS, NAT, DHCP and Parental Controls (These I've already configured these in the main router)
• Antivirus and QoS (might be useful, not familiar yet...)

Is there something important beside the ones I found, which I would (or should ) miss? Then I should still consider building the infrastructure in such way that I make the main Deco unit the primary router. I believe my options are:

1. Get two CAT5E connections to the location of the main Deco (internet + downstream to switch and from there to other network nodes) 
2. Save in the extra cable and keep the main unit in the storage room (dubious about the network coverage from there)
3. Or save in the extra cable, keep the main unit in the living room, and go for wireless backhaul to get the other Deco unit's downstream. (Only wired devices would be connected to the current main router.

In 1 and 2 the current router woudn't do much, the main Deco unit would do all the routing and network management (wireless and wired clients)

The last one would split the configuration in a bit nasty way as Deco would manage the wireless and current toure the wired. Not even sure would that work -- probabaly only running to problems with two NATs, especially if I want to give some access rules...

@daBowmore 

One popular feature would be the parental controls so if you do not plan to restrict certain devices from having internet at certain times then AP Mode would be fine. A benefit of the Deco M9 is that they have a dedicated backhaul (5GHz) in connecting to each other so I would test with and without the cable to see if there is much of a difference speed wise.

@Tony Thank you for your time looking into my case + the extensive support. I will do testing with/without ethernet backhaul.

I have currently done parental controls on the existing router, as well as firewall config + NAT forwards, so unless I would expect big performance gain, I would leave them there (just to save the effort re-creating them).

But it is definitely good to know if I want to remove the router that I can re-create everything with just the Deco.

Cheers,

Jukka

@Tony I've now played around a bit with the setup. Some notes, and questions, if you will:

1. Performance / Ethernet backhaul: I have so good results with ethernet connected that I didn't yet try wireless backhaul. I get almost full 250/50 mbps in every single location of the apartment! So performance is very good! But how can I actually be sure what mode is used for backhaul? I can't find any info in the app about that. Or quality of backhaul connection?
2. Guest wifi: the clients have full access to our private network? Can this be changed that is not really nice for guest Wifi...? Or is that only router possibility?
3. I only set one (the main Deco) as Access Point -- I think this configured all the following nodes -- at least I don't find a setting for them individually.
4. Performance is most of the time outstanding -- sometimes the Lenovo laptop has some slower type of connection -- I wonder can the nodes be interfering with each other?
5. Ping performance is also outstanding (in the range 3-4 ms), but it still is slightly slower than what it was with the old configuration (2-3 ms). While this does not matter -- I would like to understand how can this be possible -- the old configuration was 8 year old hardware, after all.
6. Does it matter in what position I mount the nodes? I'm tempted to make a mount on wall, where the unit would be then vertically -- or is that not adviseable?

Many thanks again, so far very happy on the performance / coverage gain!

@daBowmore 

1. I do not think the M9 has that ability yet, if it did, go into the app, select the globe icon, then tap on one of the nodes. If it is there it will display Ethernet or Wireless. Quality of the connection is not indicated (feature request?)

2. Right, only in Router Mode can you control that.

3. What you assume is correct, when configuring one Deco, settings are automatically applied to all nodes.

4. That or the laptop may be connecting to the further node rather then the closes, I would disable and enable the Wi-Fi card to see if that helps.

5. With the old router, you had one point to connect to. The Deco means jumping through different nodes. 

6. The wireless signal is broadcasted in the manner of the shape of the device itself so similar to a doughnut pattern. Putting the device against the wall may affect the horizontal distance, but your vertical signal should improve.