Looking good! The green is a good shade, but I would recommend something a little more pale. Try adding a little more rotting flesh to the highlights, to make the skin look more sickly. You can also add some veins by watering down some blue and red paint, and drawing them on. Be subtle with it, as it is easy to go overboard. Try adding a small amount of purple to the model, as it will contrast to the green. Brilliant work on the wings and arms, a very good choice for Nurgle. Try adding a dot of white to the upper part of the eye, and some gloss varnish too. This will make it look more realistic.
Other than that, keep practicing! You are off to a very good start. -Tarvick
Insecticising a daemon prince! Now that's a plain awesome idea. Maybe you could have intensified the overall look by choosing some tyranid legs instead of the standard ones but it's nonetheless a great miniature.
You should do it! It makes for a great project and between the other elements of the model, the way it's positioned on the base and it's final paint job it could turn out looking quite different. I'd love to see you're version of it.
Oh, I probably will... there's no reason to not have a Nurgle Daemon prince for either my Daemons or my Chaos space marines. Right now I have a Khorne Daemon prince planned first, which I'll probably make out of a Valkia the Bloody model.
But that Nurgle prince will rear it's ugly head at some point, heh.
Might even be worth picking up a box of Chaos Spawn... there's so many awesome bits in that box which make up for some really awesome conversion options.