When I initially "finished" this basemesh, I had no idea about correct topology; quads, edge loops, face loops and how clean topology is essential for weight painting. My mesh was a literal nightmare. Multiple layers inside layers, too dense and looking like a broken mirror. However, after more than a month of repair work on and off, M-66's basemesh is almost completely repaired.
I was having major issues getting the humanoid Metarig to attach to my first basemesh, and weight-painting was nigh-on impossible. Now I know why. To be honest, it's a miracle that Blender even managed to calculate a rigged and weighted model at all from the mess that I started with.
In the meantime I have also been making upgrades to my Smurflike-character Elfy (better hair, fingers, toes, tongue, teeth, and an actual body instead of just clothes.) The two completely different characters have now become linked in my mind and are the best of friends.