Stock I think is 10*. Timing is all vehicle specific. There's no specific # to set it at. Just try advancing a couple degrees at a time until you hear pinging. Then back it down to where you don't. Basically, run as much timing without detonation. On the juice I have no idea though.
As for timing with nitrous I'd check with the product manufacturer. IMO you'd want to be at or close to baseline (10*). You definately don't want detonation with nitrous.