Yes, Jimbuna, you are absolutely correct. What you suggest is the proper approach. I appreciate all your help, and your advice, which amounts to "Slow down, and start taking a logical approach."
The problem was that there wasn't just ONE problem. I had - and found - multiple problems, and putting in one piece at a time was slow work because, once I found one problem, there were still others to be found. But what got me in the end was the assumption that there couldn't be anything wrong with Commander - everyone uses it and no one has problems.
Then I finally tried Commander alone with rockstock GWX3.0, and lo! CTD! I will continue to test the Commander mods, but I'm willing to play without them right now.
I confess that a big part of my struggle was due to assuming a single problem. I tried to be too quick and did not perform a disciplined fault tree evaluation. And the result was frustration and more corner-cutting. I should have known better. Actually, I do know better, I just didn't want to do the long, dull work. I wanted to get back to playing the game! An amateurish mistake by a long-time professional.
I am rattling on like this because there is a valuable lesson here. Hope someone picks up on it and saves themselves a lot of wasted effort.