Looks generally excellent.
The only suggestions I have for consideration are minor:
1. American paints, especially those that were factory applied, were high quality and did not tend to flake or rub off except in the highest wear areas like the wing root walkways. Your paint chipping is well done, but more appropriate for japanese WWII aircraft (their paints were notorious for chipping)
2. P-51s had laminar flow wings which had all panel lines (except those for the gun and ammo bays and the control surfaces of course) filled with putty and sanded smooth, then primed and painted (even the aircraft left in natural metal finish had their wings painted with aluminum lacquer paint to protect the puttied seams - unless they had been stripped of paint in the field). To replicate this, simply do the same thing with all the panel lines on the model's wings.
3. the panel lines seem to disappear behind the decal markings. I presume you put the decals on after you did the wash for the panel lines. to make the markings seem more a part of the surface, go and do a light wash over the panel lines they cover as well now that they are safely sealed on with a clear coat. Once you do this, you'll be amazed how much more the decals seem to fit the model. (I even make a thin slice in the decals along panel lines with a new x-acto blade once they are fully cured and then hit them with another round of setting solution, but this is not for the faint of heart).
4. maybe go with a slightly darker OD on the sides of the aircraft to represent how the upper surfaces that got the most sun/weather exposure faded more. I think the color you have gone with is perfect for the lighter, faded OD (of course your flash could be washing it out and it may look darker in person, so use your own judgment)
5. the exhaust stubs are far too new looking. they would only look bright and shiny if the had never seen any time running on a hot engine. (this is more evident on your other photobucket pictures that you didn't post in this thread)
like I said, these are all very minor points, and really the model is very well done I think.
and welcome to aeroscale! happy first post.