@Cashm 

The set up seems fine.

The only issue that may come up is if the internet drops out (main Deco LAN won't know what is WAN or LAN), whatever is wired to the main Deco will have issues communicating locally. If you wire LAN devices to any of the satellite Deco units, that will not happen.

@Tony the extended plan is to LAN connect the wired remote node to a powerline as that will give me network in the garage.  So if I do that or even wire a TV via LAN from the wired remote node then it seems it should be fine from what you have said.

Sound correct??

@Cashm 

Yes, that should be fine. You can use powerline adapters to set up Deco units via Ethernet Backhaul.

If you use the powerline adapters, at least for ours there is a powerline LED light that will indicate if the two adapters see each other. So the electrical wiring at the garage needs to lead to the main circuit panel.