flywheel is a great mod. your car MIGHT try and stall out at idle, but its not very likely, especially if its stock and you havent molested the poor thing.
fuel upgrades on a stock engine are almost pointless, whoever told you that is lying.
an underdrive pully would be a good idea if they didnt like to either A) shread timing belts or B) cause balance issues.
Cams are a great idea, but then just adding a new ecu isnt gonna cut it, cause you are going to want to retune that engine for the cams you just bought. you will thank me for that advice, believe me.