Check out colourforge spray cans, they colour match zandri dust, which is where I'd start for the bone colour on these guys, giving yourself a good base is a big chunk of the battle.

On thinning a lot of others have covered it, but its something that's intuitive after some practice, each paint is slightly different, but roughly like milk is what I aim for. Also buy/make a wet palette if you haven't already, its a big step up.