Not bad for a first attempt!
I am no super expert but I did paint some 50 chaos models with
NMM weapons and details. From my experience I would advice you to be a bit bolder with the contrast on the gold. Always really pure white on edges facing your imaginary light source (usually up) and make the dark parts even darker.
As for the SENMM i feel black for earth is a difficult choice. A warm color like some shade of brown is easier for the eye/brain to understand.
For me it took at least 10 models before I was even getting the idea, so keep trying!