Kits are def. the better buy as the parts are all VERY pricey. Yeah, nitrous CAN be done on the cheap, but to do it right costs $$$$$. I have between 1100 and 1200 in my set up. If you need a remote bottle opener I have a spare one New in the package I can sell you, otherwise I'm using everything else.
Speed is only a matter of money; how fast do you want to go?