Your technique is good, and your designs are unique. Very creative. On a technical level, I might cut the insertion tab off the missile pod in the top picture. It looks messy just hanging down there.
On a personal note, I don't dig this color scheme. I think that corrosion, battle damage, and dark colors don't really fit the whole Tau schema. The Tau are set up to be a dynamic, vibrant, energetic army, and these details lend it more of a war-weary, gritty vibe that is more at home with an Imperial Guard army. I don't think it really works with Tau, but that's just a personal preference, of course.
If, however, that's the kind of look you were going for, then you achieved it in spades!