I'm not the greatest converter either but as a Nurgle advocate I feel it's something you need to do to make it Nurgly and authentic. Just practice with green stuff, that'd what I'm doing at the moment. Pictures to come soon on my PLOG - anyway, back to your army....
I'll check out your PLOG when I get cap, it'll be good to see a fellow Nurgle Army
Would you count bikers as foot soldiers? technically not on foot but not really "vehicles" in the sense either, plus nurgle bikers are T6 which is delicious, and you could probably convert them to be riding something nurgly, instead of bikes....
Bikes are Fine, so that could work.
Worms, for instance...easy made with greenstuff
But this could work a whole lot better, only thing is I'll have to make them fast worms