Gerry, first I want to say congrats for getting things setup; even if it was done in an unorthodox way. I have to say, I found it confusing trying to follow all your steps; especially with mac-speak sprinkled in.
Now, let me explain how it ought to be set up so you can work toward this end as it likely will clear up some of your remaining problems.
I want to keep this to bottom line basics; no matter if a Mac or PC is the computer used. To keep this simple for now we have a router, a computer and a My Cloud NAS, all in the same room; even all on the same table. Everything will be wired to router via Ethernet cable and the cables from the computer and MC are plugged into available ports on the back of the router. Everything between the three devices will be working at maximum speed among the three. Setting up the MC should be a snap (unless there are issues like the computer OS prevents this from happening as you first mentioned. So for our example here let’s discard that issue, so we have our perfectly installed setup.
So now, let’s bring in other devices to the network, like phones and tablets that can connect to the network. Setup properly and with the My Cloud app, these mobile device can easily connect to the network, and, to the NAS, and the computer. Let’s imagine there are already some media files on the MC, and likely there are in the Sample Media files pre-installed on NAS, and now all these files can be streamed to the computer and mobile devices through our table top network.
But, we have an issue, you may say there is no way you can keep these devices all together on a table top, because the router needs to be elsewhere (perhaps be more centrally located in house for best wireless coverage). So you move the router to where it is supposed to be (likely wired to modem and incoming Internet signal.).
Your NAS is a wired device only, so it goes where the router goes, and is of course, Ethernet wired to it. Laptop can be connected either way to network.
All this to point out that the wiring and connecting of these devices in some cases is precise, and in ways optional. And, it all boils down to being simple.
In my case, my house has Ethernet wiring in the walls for four outlets in four rooms, so my NAS and PCs are on one side of the house, and the router is all alone, connected to modem and the CAT5 connection box. Nevertheless, they are connected as they are described on the table together, because the wall outlets, and network switches used have the same affect as a table top setup.
Envision your network down to the bare bones, and again, it is simple at the root of it all.