You can get one of the Zex Venom kits pretty cheap these days. I'd suggest that you stick with a 55 shot to be safer. You can go with the 75 shot, but I wouldn't recommend doing that alot on a stock bottom end. When you use n2o, you will definately need at least 1 step colder plugs, maybe even 2. An ignition system would be a great idea, and good fuel management. You might also look into getting a wet shot nitrous kit. Those mix the n2o with the fuel before spraying it into the combustion chamber. Also, getting some good cams would be a great way to add some power. Don't get too agressive of cams unless you plan on upgrading the rest of the valvetrain, but it's another option. Once again, tuning is the key to having an effective and safe n2o system. I know this has been quoted many times on here before, and is in at least 1 persons sig, but it is the truth:

Nitrous doesn't kill motors, stupid people with nitrous kills motors.

Remember that tuning is always the key to a reliable setup, and take the time to do it right.