Mud is mud. There are different ways to achieve a mud effect on models - drybrushing, pigments, paint and grit goop, etc. - but it's the same deal, regardless of the underlying color (ignoring the different
types of mud, which, of course, vary somewhat in their ingredients). Tutorials abound, once you stop looking for something unnecessarily specific.
As for the white, sadly, you're in for the long haul. Honestly, for
BT you really will save the most time by priming black, so get used to building up your white in layers.
I'd recommend picking up a pot of Astronomicon Gray if you don't have one. Working up through shades of gray to your final white color works, but Astro. Gray is a very light gray as well as a foundation paint, which will help you get a light and neutral base for your white in less time. Personally, I go right from black spray to Astro. before starting my coats of Skull White. Properly thinned (i.e. as thick as will go on smoothly), it only takes a few coats. I'm usually good to go after only 2 or 3. I use it to basecoat for all of my light, don't-cover-for-crap colors - white, bone, etc.