My understanding is that if you see RPM on the tach, then the CPS is working. No CPS= no RPM on the tach.
To test a spark plug you can just take one out and look at it while you try to crank the car. Be sure to hold it with something insulated or else the spark may get you. Harbor Freight also sells a little device that the spark plugs screws into, and then you put it in the spark plug well, and I think it lights up. I bought it when troubleshooting my son's Ford Ranger no start problem (turned out to be a g-force fuel cut off switch)
However, the wheel/notches that turns that the CPS looks at - does it come off during any part of the process? The reason I ask is that on the Miata that wheel does come off as part of a timing belt change and if you put it back on backwards you get RPM and spark plugs firing, but at the wrong times so the engine doesn't start. Flipping that wheel around and it started right up. I could be way off base. [Edit I just looked up some parts diagrams and it looks like I am way off base here
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Good luck.
Steve
On the other, I went through the same thing in 2009 - it was a rough time filled with a lot of self doubt. There was no reconciliation and ultimately things got a lot better but it was a rough time. Best wishes.