Looks like a fun list, full of blobs and a few tough units. Though there are a lot of areas you could save points, and keep to your theme.
For starters I would say to never put marks on your Cultists. The +1 toughness is not worth the cost per model, especially when you could just take more bodies instead. Besides, if you want tough Cultists just go the Typhus route and run them as Plague Zombies instead. Also, shotguns are rarely worth it. I've never found myself in a game and thought "Dang, that shotgun would have really made the game!". Heavy stubbers are not so bad, but you should be snap firing them all game, so take that into account. Flamers never miss with a template, but that's just my 2 cents.
Like you mentioned, you went a bit crazy on your Lord, heh. I tend to do the same, it's so tempting. Though 285 pts is A LOT of your army. Particularly Ichor Blood on both your
HQ's. Additionally what is your plan for the Lord on the Palenquin? His mobility will be hampered if he runs with the Cultists, and he'll just be picked off if he runs alone.
If you did plan to run the Lord with some Cultists I would suggest dropping the Nurgle marks and making one huge blob for your Lord. Would be pretty cool thematically too, a mighty Chaos Lord on his mount surrounded by a horde of shambling Cultists.
I mean, besides all of that WARHOUND!!! So in either case, that should handle most lists

.