How should I plan for a VP win as Nurgle?
Nurgle's general best winning strategy seems to be to go for VPs, not ticks. Khorne goes for ticks, and the other 3 go for either or depending. (This is actually suggested in the rules, near the end in a 2-page spread about strategy.)

In short: dominate all you can partake in every ruination. Those provide the big points.