Sublime work OP. Love the sheen control, the glossy coffee.

Since they're clearly a warhammer 40k fan, a recent discovery of mine for mini painting: artist gouache or artist watercolor are awesome for pin-lining and recess shading the way oil paint or enamels are often used for those tasks, but only water is needed instead of white spirit. And they're indefinitely "editable" with a damp brush / qtip. The only downside is that you need to varnish to seal the watercolor before painting over it. A black and a burnt umber alone will get you really far. Make sure the gouache or watercolor use a gum arabic binder.

Demo of the technique from 3:30 - 5:20 (strong Italian accent warning, closed captions help me): https://www.youtube.com/watch?v=7vHDq3NJj4E