@ricmor555 Yes this is nearly identical to how mine is...  I have three X55's which were a mix of wired and wireless backhaul at some period in time... but they're all back hauled now... but I also have X50 outdoor ones in the same mesh with those and one is wired backhaul and the other is across the yard on my shed (pure wireless), connected back to the other backhauled x50-outdoor on my garage (via WiFi as it's an "island" out there. 

so I say yes it's no problem... the ONLY part of this I'm not 100% on is where you have the one node backhauled to the middle node (which is not the main node)... and then that goes backhaul to the main one at the modem.

saying: I'm not certain if that's cool to do or if the wired backhauls all need to home run back to the main node (or a switch connected to it).

that is, all satellite nodes in my setup are run back to the master/router mesh node, rather than run to/through any other satellite nodes.

I read some potential about creating a routing loop if they're connected in a specific config but I cannot remember what that circumstance is.

is it not possible in your diagram to have that one satellite node run back to the main one, instead of to that other satellite in the middle?

just asking, wondering if it's impossible due to cable limitations/availability or if that was just the easiest way for you. 
 

honestly here's a thought for you to consider— I have a two story house and a post-construction garage with no Ethernet runs and it's pretty much impossible to pull any cable without crawl spaces and access between the buildings.

I had this totally desperate rigged setup where I was using powerline adapters to get hard wire to these node locations because my house is solid brick and you'd go on the other side of the brick wall from a node, on the outside of the house and it killed the signal dead almost.

The powerline solution just BARELY worked and I was able to get a barely usable 10mbps throughout to my outdoor mode to feed my security cameras and shed. 
 

It was just overall garage and a total hack job that barely worked but barely was better than nothing at all.

long story short, I realized I did have coax cable run to tv outlets through the house and garage and I wasn't using them. Bought MoCA adapters and hooked up each satellite node backhaul through MoCA/coax and omg it is amazing.

Anywhere in my house or on my property I can get like 950Mbps over WiFi to my phone or computer or whatever. I get the full down/upstream bandwidth of my internet connection over WiFi no matter where I am. Wired connections are just as great.

and with the mesh system (x55+x50 outdoors) I get full WiFi signal everywhere I go so my point is --

Deco mesh + wired backhauls over MoCA is frickin AMAZING. I went from constantly dropping WiFi due to poor coverage and even when I could get connected I was getting like 10-30mbps... a tiny fraction of my gigabit fiber.

now I get the same speed over WiFi while I'm way out in the yard or my outbuilding as I do taking a laptop and plugging directly hardwired into my isp modem.

so all my woes are gone and everyone who uses wifi at my house is like HOLY... !!!

  @ricmor555 That is a perfectly valid configuration.  You can mix the various types of backhaul.

The main restriction, in Router mode, is that one Ethernet port of the main Deco must be exclusively used to access Internet.  Nothing else (no Deco, no device) can be accessible via that port.

  @yves_b @YourStupid  Thanks for the responses.  Very helpful!