@GR1 

1. How do I wire backhaul all of these into the same network?

That mainly depend on your physical environment and where the Deco and devices are located.  The usual practice is to install cables in a star configuration, all cables originating from a single location, where you install one switch.  If you have several devices in the same location, it is usually prefered to use a switch at that location, instead of using multiple cables to the central location.

As your Deco mesh runs in Router mode, you must directly connect your main Deco to the Starlink box, without an intermediate switch.  And use the other ports of the main Deco to connect to the other Deco and to the devices.

The devices can be plugged into the main Deco or to satellite Deco, directly or via switches. 

2. Is there a certain switch / switches that need to be used? The three, X50 Outdoor access points are PoE capable.

Do you require or prefer using POE to power the Outdoor Deco?

3. Is there a switch with enough ports to handle this and will also accommodate an NAS, NVR, 2 computers, a printer and connections for 2 smart TVs? Assuming would need to be a smart switch that has function to turn on / off PoE, or do I just add a PoE switch to one of the 2.5 gb connections on the BE85 router?

There are many large models of switches, and you could as well use several switches.
Many "POE" switches have non POE ports and POE ports. POE ports are usually more expensive.

You can connect a non POE device on a POE port, the switch will automatically detect if POE is used or not. 

  @yves_b 

Thank You for the info. That really helps. So if I understand correctly. To mesh the different Decos together wired and since some are PoE+. I can either:

A. Example: Obtain a 24 port PoE+ switch (plug it into my 10G port on the Deco BE85 router) that I can plug in my PoE+ devices, and also plug in my non-PoE devices to the same switch and let auto-sensing not supply power, or a managed switch that I can turn the power off to those ports.

B. Example: Plug a smaller 5 or 8 port PoE+ switch into the BE85 10G port to run my PoE+ devices. Then plug a 16 port Gb switch into one of the 2.5G ports of the same BE85 Router and use that to power my non-PoE devices.

C. Example: plug in PoE+ switch into BE85 Router. Then plug Non-PoE switch into that router (tether) style and use that way (which is probably the least desired)

I understand that if using all gigabit switches. I will only get gigabit speeds or less (whatever my ISP - Starlink supplies).

Thank You.

  @GR1 You can indeed do any of what you describe.

If you are building an house, the most important is to correctly setup your Ethernet cabling.  In such a way it can be used for your current usage, and for future usage.