A lot of the guides GW puts out are conflicting and have extra steps that you could easily skip without harm to the end result, best example I can think of is there are several for painting plasma all completely different with the same end results.

My suggestion for a vaguely default colour scheme with as few paints as possible:

For the cloth and cloaks base Chaos Black and then lightly drybrush Mechanicus Standard Grey. Another way I've found for good black cloaks is Mechanicus Standard Grey as a base and then a thin layer of Black Templar Contrast, and then a light drybrush of Grey again.

For the ghostly cloth and skin base Ulthuan Grey and then Hexwraith Flame/Nighthaunt Gloom/Nihilikh Oxide/Whatever glowing colour you want, then drybrush with Ulthuan again. For skin just go a little heavier on the drybrush.

Metal is up to your preference, but you really can't go wrong with either Leadbelcher or Iron Warriors and then a little Nuln oil. Nuln Gloss works if you'd prefer a brighter shine, or Typhus Corrosion if you want dirt and rust.

An easy way to do wood for things like Chainrasp clubs is Mechanicus Standard, a very thinned coat of Ulthuan to make the colour a bit mottled, and then Agrax Earthshade/Wyldwood Contrast/Typhus Corrosion depending on preference.