I don't know what you're talking about, Beasts are
lovely to play against!
:
Don't stick Epi with the Plaguedrones - they'll be lumped with his lower movement and die.
Don't stick him in Plaguebearers, he'll be targeted, and doesn't benefit from LOS! due to different unit type.
Hide him as best as you can. He's fairly handy on his own, so should be able to handle most chaff that gets thrown at him.
Also, ditch the Daemon Princes, they're really not worth it for DoC in Fantasy.
Best advice would be to bulk up the Plaguebearers to a unit of 40, bung a hearld with the Regen locus in there, and another as BSB, both Level 1. Take level 4 on your GUO and take an Exalted Gift - if you roll anything other than a 6, take the Eternal Blade. If you roll a 6 take an Eternal Blade and whatever you rolled on the lesser table (hopefully ASF for maximum enjoyment!). That gives you all the spells of Nurgle, and you're looking to get off the Curse of The Leper + Rancid Visitations combo.
I find 2 units of 3 Beasts to be VERY effective, but other people claim running them individually. Probably best to have a play around and see how they work for you.
A Soulgrinder is definitely worth it if you're running an Epi list. Give him either the Stonethrower upgrade and sit back, or give him the flamethrower and run him forward. He's got high toughness, a 4+ AS and a 5+ WS so should be alright as long as you don't bog him down in a unit that has a high level of static combat res, and his weapons let him get the tally going Turn 1.