NOS
Until then, stick with 100-125 max, to be safe.
What kind of car do you have, M6 or A4, gearing, mods, race weight, etc etc. Also I would read up on the differences between wet and dry systems.
The people that blow up their engines are the ones that do no research on nitrous. Nitrous isn't something to be taken lightly, if you do something wrong, you WILL seriously F up your car. Use the search feature, or just browse around in the nitrous section to learn about the different types/kits/applications, and find the one that fits you the best.
FWIW ... a completely stock car, with a 100hp dry shot, will be pushing around 380 rwhp ... track time would depend too much on the varibles you have not yet stated to guess at it.

