holy wow.
1- put a colder plug in the car gaped at .035 minium 1 degree colder recommended 2 degrees colder (Motorcraft part # AWSFA12C, there about 2 bucks each for the same perforamnce that thoes 10-13 dollar plugs your talking about, thats what i have in my bird)
2- have a rpm activation switch
3- Bottle heater you want to always run the bottle pressure at the same pressure everytime, most recomend around 1000psi
4- pressure gauge duhh
5- blow down tube
6- fuel pressure safety switch. kills n2o when/if fuel pressure drops
7- purge, this isnt for show, it does serve a purpose. You want to have nitrous at the solenoids ready to be injected into the intake, if not youll have fuel being injected without the nitrous for a split second and that could puddle and cause you bad things. You want to have a balanced mix of nitrous and fuel being injected at the same time.
8- get a good tune done, if you ping you will blow the motor, get one of the SuperchipsCustom.com multi position chips with your mods programed and youll be ok. they will run the correct timing for your nitrous program so you will not need a timing adjuster, actually they tell you to take thoes off because they program their chips with additional timing and retarded timing based off of the stock timing.
9- DO NOT USE THAT NOS OCTAINE BOOST CRAP it dont work, when they say it raises octaine by a point they dont mean there taking (in your case) 91 octaine and your then getting 92 they mean there going from 91 to 91.1 read the bottle.
10- DONT GO CHEEP ON ANYTHING YOU BUY nitrous is dangerous when not done properly, dont cut corners, if you do you will be putting a new motor in the car, BUT, it sounds like your on the right track.
as far as you only having 91 octaine in your area, thats ok, a good tuner can take that and get you the right tune so that its safe and powerfull, so dont worry there. it sounds like the package with add on that you posted is going to cover most of the things i mentioned above. just make sure your not stupid with it. im running a 90hp kit from CompuCar and it droped my et 1.5 seconds im running without the rpm activation switch right now i do have an automatic so im not worried about the reving the motor to the rev-limiter mine shifts at 5500 all the time everytime, if i do go over that it means i have other issues to worry about. I do plan on geting the activation switch just to make it more consistant 3k on 5500 off.