Ok, let's start with eyes. Eyes are refuckingtardedly troublesome to get right in this scale. There is no "one right way" to do it, it's all circumstantial to the sculpt, that will determine how to go about doing the eyes. Sometimes I use a very small brush, sometimes a blunted toothpick with a dab of paint, sometimes i use a .005 micron pen. Sometimes I even paint the eyes black and then paint white in layers around the iris, then do a dab of very washed paint on the iris, then use a small brush to darken the pupil, then a super tiny brush to add a couple of dabs of white for highlights..
What worked for me is I took a bunch of (5-10)random fodder heads I didn't give a shit about, hand painted/primed them all black, threw some quick flesh tones on them, and then concentrated solely on the eyes. Different sculpts require different approaches. I dunno man, it's all about practice.
Oh, another thing, the top eyelid should always cover a bit of the top of the iris or the face will look super surprised and kinda cartoony.
On to paints...the thing about paints, always go in thin layers to achieve super smooth results, and from what I can see in your pic's, you already do, they look great. To make all the details on the sculpts pop a bit more always drybrush a bit. Even if it's flat black base, lightly drybrush a grey or tan over that, just to make the shadows and highlights more dynamic.
Also to accentuate the details paint buttons, zippers, buckles etc. a different color than the pouches or whatever they're attached to. Silver though is generally used only to weather buckles/firearms and what not, but not used as the base color.
As far as parts go, you're super solid, I really dig what you've come up with. Maybe just flip RnR's box mag around, it's backwards. The side of the mag with the cut corner always goes on the shooters right, just like Leathernecks. Unless it's a lefthanded setup I guess.
Oh, last thing. The key to good pix is a lightbox. Screw buying one online, just build your own for a fraction of the cost. Get a cheapo clear storage tub from Wallyworld, cut the front and sides out, but leave the vertical corners for braces. Flip it upside down, throw a super thin white cloth over it, a couple of cheap spot/work lights on the sides....boom, lightbox. I'll pm you some pix.
Again man, this what I've found works for me, I'm sure there are better ways but...I'm still/always learning too. Sorry it took so long for me to respond to your pm, real life stuff and all.