Nitrous Express...

I decided to do the nitrous express kit for my 99 gt. How much of a shot would be safe on a completly stock gt? And, is there anything I should upgrade before I do it? Thanks for all the help.

EDIT

http://www.mustangtuning.com/niexfoefikin.html

Thats the kit i'm looking at. Do I need the accessory kit 1 or 2?
http://www.mustangtuning.com/nitrous.html