Hey! Nurgle
CSM is awesome with daemon allies, I've actually just put together a 2000 pt. fluff list as well.
A few changes that I've found work really well bring out a few great synergies in the Daemon codex.
In my fast attack slot for the daemon allies I use a minimum squad of plaguedrones, one with an Icon of Chaos and one upgraded to a Plaguebringer with a single lesser reward for the AP2 Etherblade. The whole squad also has the 3+ poison upgrade (which adds it to the etherblade

) they come to 171 points, the box is around $40 (canadian) i think but it has the full squad in it at least if you did end up purchasing it.
I also give my squad of plaguebearers an instrument of chaos, literally the best 10 points you could spend. Hold them in reserve with your
GUO seperate but also in reserves. Roll for the Plaguebearers first and if they make their roll you get your big guy in for free! This effectviely gives your
GUO 2 rolls to try and get in since if the plagues dont get in he still gets his own roll.
This is where the Icon on the Plague drones comes in. They move 12" then assault move
2d6" turn 1 and then on turn 2 you drop big ol'
GUO 6" away from them with NO SCATTER
I've found this really effective because it gets him mid field waaay faster and far more reliably than walking 6" a turn especially with Slow and Purposeful.
If you dropped each of the plague marine squads to 7 (which is super fluffy haha) you'd have just enough points. Also, if the Lord has melta bombs you might be able to drop the bombs on the biker champ, that would also save you 5 points if you needed it.
Keep it sleezy