Nice to hear you got beautiful results
1. This means "let's assume the I-V curve is symmetric", so if you only computed the current for positive bias values, the plot will also include I(-V) assuming it's equal to I(V)
2. Time is not an element in these calculations, but you can simulate the static influence of traps. You just need to replace or remove some atoms in the interface.
3. Not really.
4. No. What kind of script? It wouldn't really make sense, I mean, what data do you want to pass from Matlab to ATK?
5. Not sure, can you describe in more detail what you do? It should work.
I'll answer the final question by mail