I've just built and primed some GW Orks from Kill Team Octarius and some of the Ork character models from last year.
Touching up the primer was a royal pain, and painting some areas will be pretty much impossible.
I have started to wonder if I should have gone for sub-assemblies, but one of the problems with building the Orks is 140+ parts spread randomly across three sprues (to defeat the box splitters, so I've heard). Arm down to the wrist, then separate wrist and part of the hand, with the rest of the hand holding a weapon that's in multiple parts

The fit was generally excellent, but two parts did need some filler (not sure it that was GW or my gluing), so I imagine that would be unpleasant if everything was painted before discovering that.
I still don't know what the answer is, but your appoach is definitely one I shall consider for models with small part counts.
On that technique, do you just basecoat before building, or do you do the full shade and highlight before reaching for the glue?