yeah, i started with the rsx type-s, and just kept doing the drag races against stock cars, and a few ricers, and just kept upgrading little by little. i kept finding new oponents that i knew i could beat. the H2 in the tuner (i think its this category. its the 3rd category...right under ricer) category you can beat with a stock rsx. and then you get $1000. after i built up my car a good amount, i started the story. and you get money quick with that if your car has decent mods.
for the nos, i use is about 75% through the race, and only if im on the cars tail. if im too far behind, i just let him win and not waste the nos. then go to return, instead of retry, after the race, and pick a different car that i can beat easier.