@IzIFRag 

Let's start with basics of Deco mesh and WiFi mesh deployment.

Deco creates its own WiFi network and mesh, it does not extend provider's router WiFi network. For that reason, it is recommended to turn off WiFi on provider's equipment after Deco mesh is deployed.

With that in mind, you'll need to figure how to place Deco M5 nodes to provide WiFi coverage over the whole house. You won't be using provider's router WiFi to complement Deco WiFi.

When Deco nodes communicate with each other over Ethernet, in Deco terminology it means they are using "Ethernet backhaul." More information about that and its limitations can be found here: General questions about Ethernet Backhaul feature on your Deco.

Deco mesh can run in Router (default) mode or in Access Point mode. The difference between these two modes is described here: What’s the difference between Access Point mode and Router mode on the Deco?

I would recommend for you to run Deco mesh in Access Point mode. In that configuration, provider's router manages the network, like it does now, Deco provides WiFi mesh coverage. Also, in Access Point mode you have absolute flexibility in Deco nodes deployment: you can connect Deco node to any Ethernet port or cable in your house and it'll work properly.

This is how I run my Deco WiFi mesh, which consists of four Deco nodes: two M9 Plus and two M5.

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Reviewing your options.

In all three options, Deco will establish WiFi mesh, and all the devices, wired and wireless, will be in a single network. Options 1 and 3 will only work with Deco in Access Point mode, Option 2 will work with both Deco Access Point and Deco Router mode. I would not recommend Option 2, for multiple reasons. 

As I said before, I do recommend configuring Deco to run in Access Point mode. After you set first Deco, which will become your Main Deco, change its configuration to Access Point mode, in Deco app, and add remaining M5s to the mesh after that.

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Deployment hint: each Deco has two Ethernet ports. This can be used to place Deco where you already have another wired device. For example, I found a good place for one of my Deco nodes to be at my TV stand in the living room. TV is Ethernet wired. I took that Ethernet cable and plugged it to one of Deco ports, used another Ethernet cable to connect Deco second Ethernet port with TV Ethernet port. 

Same in my home office, Deco M5 near wired network printer "borrowed" printer's Ethernet cable and printer is now connected to the second port of that M5. All I needed for that to work is spare electric outlet to plug M5 in. 

I can see from your drawings that your house is nicely wired, so you can do the same where you already have wired device and want to place Deco unit, too.