First question:
The beginning moles of N2 and O2 have to be zero as they are the products.
Second question:
When 40% dissociates there should only be 60% left, hence 0.60, and not 0.80.
Because the steiochiometric equation is equal, the amount reacted for the products of this reaction should be +0.60 moles. And not 0.40 moles.