Looks great dude.
I personally wouldn't seal it, I assume those are AK enamels used for the pin wash? If you are gentle with the thinner (like a very damp brush, not 'wet') your next application wont effect the first.
Try using another color, but not everywhere, just a little corner there, around a few bolts here, then let that dry overnight.
Repeat this a little here and there, very subtle, very slowly. Once you begin to get accustom to how the products react as you work with them, you will be able to do more in one sitting without washing it all away.
Remember, its always easier to just add a little more than it is to take too much off. You're off to a great start man, just go slow and easy, and apply a little each time.