I am no pro for sure, but I have painted easily 200+ plaguebearers so I know how to do them fast and for the table. If you\'re looking for better quality then what I have presented here then there is no shortage of good advice to be had from some top notch painters. I would reccomend starting on a couple, post pics and WIP on these forums and ask for more specific comments and advice. Anyhew when doing basic skin I tend to use the equivalents of Bronzed Flesh, Rotting Flesh, Codex Grey, Snot Green (Not much!), a little purple every now and again, Scorched Brown, Leprous Brown and that sort of a thing. I am also a big fan of using the new Foundation colors whereever I can.
I start by painting a model in one of the darker Browns, Greys, or green and then sort of overbrush (drybrushing with much more paint, and not very carefully at all) in lighter colors until I get to a result I am happy with. I have used thinned oil paints fro wahses on these guys but I am sure you can do an approximation if you like by washing the models heavily with different browns, black, greens, purples or whatever in patches on the model. Best part about doing a nurgle themed army is that you can really experiment on color choices without having to spend the amount of time on accuracy you would with some \"cleaner\" armies. This is what I wound up with....
I am happy with these guys for the table, but you will get better color choices and advice from others. Good luck!