Nice list ! It looks Nurgly and fun. The only thing I'd wonder about, is why you'd make the most important Herald (well, one of them) - with the BSB * NOT * on the Palanquin ?
IMHO the Palanquin // Noxious Vapors // Herald Lv.1 with Miasma of Pestilence, combo is one of the deadliest in all of Warhammer.
You get a 6+ Armor Save (

), but more critically the SIX extra Poisoned Attacks from the Nurglings holding the Palanquin....and that, coupled with the Noxious Vapors allowing the Herald to strike first - PLUS - the Standard of Seeping Decay allowing re-rolls on failed Wounds.....means you can deal a tremendous amount of damage with that one model.
Even worse, when you have the Lv-1 / Miasma threat every single round, you basically ensure your opponent will have to use 2-dice per casting attempt by you (or more) - to stop what you roll.
I often "1-dice it" with Miasma, and have a 66% chance of casting it. If you throw in a second die, you really jack the %-success up, and guarantee they must use 2-3 Dispel Dice / Scroll to stop it.
Why must they stop it ? Because if it goes off, its essentially an "Infernal Gate" instant-kill on the enemy model or unit you are facing.
By making the front rank (touching the Herald) all reduce to WS-1 , T-1 (the main stuff for our attacking purposes), you ensure massive carnage from the Plaguebearers / Herald / Palanquin's attacks.
Everything will hit on 3+ and Wound on 2+ (with re-rolls).
Also, remember that as Casualties are taken, you replace the slain front-rank models with those from the rear ranks (normally you can wait till the end of the combat round to remove losses, and fill in the holes, - but TECHNICALLY it's happening "as the models are slain").
This means that once you've taken down the front-ranked models (usually 4) that are initially touching your Miasma-spewing Herald....4 more replace them, and are immediately knocked down to that same WS-1, T-1, reduced profile !
This is why, if you roll well, you can effectively knock out 10+ enemy models from a unit, as long as you got the Miasma off. This will destroy many lesser units utterly, and result in them losing the combat, if nothing else - if they are a larger block.
Assuming no ItP or other abilities, you will break them and have a chance to catch them while they run.