I have a
thread on Nurgle you may find helpful.
For list-specific advice; give the monks blade+staff since they will deal more damage that way with Glottkin (they get +1 attack to each weapon profile) and split them into two 10-man units to minimize battleshock damage (and get two unit champions with books). Give your daemon prince the chaos talisman artifact to help keep him alive since he is extremely important for the Drone locus.