1) yes sir, for goblinoid skin as an example I use the dark Gnarloc green (foundation), then the lighter goblin (warboss), then the bright scorpion (the moot) followed by a bright yellow highlight.
I usually use a red foundation under red too, though the current "Evil Sunz Scarlet" is nice and thick.
2) I think so, I try to be as neat as possible but often find little overlaps or missed bits- usually after taking a macro photo
3) Kind of relating to 1 and 2, I undercoat any yellow with foundation yellow (Iyanden darksun) and then put golden yellow over the top in a couple of applications.
A liberal dose of Cassandora Yellow wash or shade at the end works brilliantly- I don't highlight yellow.
Obviously I use Citadel paints, and I still have the old Bad Moon Yellow which is an absolute mongrel to work with on any substantial are- I only really use it for highlighting Goblinoid flesh.
Amusingly, I think your Mummies look ace!
edit: try using foundation yellow as a basecoat for gold, which is another tricky consistency in my opinion.
It's best to work off a palette and add water instead of straight from the pot- especially when attempting tricky colours like yellow or flesh.
As for human flesh, here's roughly what I do ( working off a black undercoat )
* dwarf flesh (now ratskin) in thin applications, may take a couple of goes to get it consistent over the mini
*liberal dose of flesh wash, let it dry
*re apply the dwarf/ratskin flesh as before
*50/50 mix of dwarf/ratskin and elf/kislev flesh, leaving the "corners" (under the hairline, jawline etc)
*highlight raised areas with elf/kislev flesh
*final application of watered down Ogryn Flesh/Reikland Flesh
I should mention I never paint lips or nipples especially, the washing process takes care of them.
If you do though, a good tip is to not paint the top lip.