One of the best (IMO) things to do is to research your a/c if you can.
When was it used? (will help determine what was available for materials for paint, and the quality of the paint, how fawst did it need to be painted?)
How often was it flown? (more air time = more wear & tear)
What theater did it operate in? (a sandy African plane would have different wear then a late war, muddy dirt field Easter front plane, etc)
I, personally have about 50 layers going (I make a copy of a few to see how different changes look immediately without having to undo a lot. I just turn the different layers on and off)
Weathering is a personal preference, I guess) I try to approach it like it would happen in real life. i.e. Primered, 1st coat of color, 2nd coat of color, top coat, etc. Instead of adding the weathering (for the most part) I remove it.
With each above layer of paint (as mentioned above), I start erasing my weathering and exposing different layers of paint in different degrees, just like in real life where paint would wear, layer by layer.
Also don't forget about the ground crew guys opening/prying hatches open, putting wrenches to things, and walking on the plane.
As for my opinion, I will agree that the black is much too dark as well as the other observations offered. It's not a quick or easy process.
Also play with the material file (No offense to HTC, but the default is too cookie cutter) On the other hand, if they tweaked each and every one, what fun would be left for the skinner guys?
The best advice that was given to me which , as time goes by, I realize to be true is.... DO NOT RUSH the job. There is no hurry to submit it. Most guys will respect the fact that you have called "dibs" on a skin. Another thing is to just walk away from it for an hour, a day, a week. You will get a different perspective some times.