So for the part about how to activate it, use a few switches.
First switch = on when gear = 3, 4, 5.
Second switch = on when TPS > 90%
That way you can keep it easily under control and only have nitrous when you are sure you want it
EDIT: There is no reason for it be a bomb. Use a progressive wet kit limited to a 60 hp gain. Run 1 step colder plugs and only 91 octane fuel. Shouldn't cause too much issue over time.
The reason nitrous = bomb, and so many nitrous motors die is people who have no clue what they are doing running big dry kits with no supporting mods usually, or going for 200-300+ shots on motors.