If I was in your position I would either go with a Zex Dry kit, or NOS direct port, where each intake runner has it's own fogger nozzle spraying fuel and nitrous. The direct port will give you the versatility to go with higher than a 75 shot in the future if you want. 75 shot is the lowest you can go on the direct port kit, and your motor can easily handle it. However, the install is a little more involved as in you have to remove the intake manifold and drill into it. If you don't wanna go above a 75 shot, the Zex kit is perfect. Easy installation, use, and tuning, very safe when properly used and tuned. It's the one I run.

As for using it, you can use it in first as long as you are above 3000 rpm, and assuming you have traction...just don't hit the rev limiter. Generally people don't spray while in 5th gear, its kinda pointless anyways.

Besides the nitrous kit, you'll need a nitrous pressure gauge to monitor bottle pressure, and you'll probably want a bottle heater to make sure that your pressure is always optimal, between 900 and 1100 psi. Below 900 you won't really feel much of a kick, and since you live in Chicago its gonna get cold, and your pressure will be low. You'll also need 1-2 heat range colder than stock NGK copper plugs, gapped to .030", and you'll need to retard ignition timing accordingly with your shot size. Your car will easily handle the 75 shot, and will love it.