A suggested list with most of your choices and some additional ones:
300 Ku'Gath
110 Epidemius
110 Herald of Tzeentch, Bolt, Chariot, Legion,
MoS
245 7 Beasts of Nurgle
105 3 Flamers of Tzeentch
210 14 Plaguebearers
105 7 Plaguebearers
105 7 Plaguebearers
48 3 Screamers of Tzeentch
220 Daemon Prince - Wings, IHide,
MoN, Gaze
220 Daemon Prince - Wings, IHide,
MoN, Gaze
220 Daemon Prince - Wings, IHide,
MoN, Gaze
1998 points
An all Nurgle Daemon list is of course the coolest thing in the
WH40k universe, so I get what you're doing
Thing with Nurgle lists is a Huge lack of mobility and a disturbing difficulty with armour. You allready opted to mitigate this somewhat by introducing Tzeentch Flamers. That may be a good start. At 2000 points you can afford this luxury. At 1700 points I would hesitate introducing a non-Nurgle unit because of the importance of the Tally to the functioning of the list.
Things I would change are given with the abovementioned list. I'd refreign from using a Soulgrinder. Im not a fan of them in any list, but in an Epidemius list I like them even less. The Nurgle Princes need Wings
IMO. Their mobilty offers a possible threat to vehicle that you really need. I suggest Beasts of Nurgle because they have the benefits of Plaguebearers without the Plaguebearers most flagrant weakness: the inability to deal damage in
CC. The suggested Herald of Tzeentch is meant to offer mobility and some anti-tank. Same goes for the Screamers who are increadibly cheap for a unit that can contest an objective last turn with a 24" turboboost move. In theory it can threaten a tank so the unit isnt even wasted before the contest move.
Good luck with the list. Let us know you you fare with it.
Cilithan
Daemons: 5000+ points
CSM/Black Legion: 5000+ points
Deathwatch/Knights: 5000 points