What aftermarket parts?

[Redryder]

Hi i have a 98 kawasaki xi sport its completely stock i would like to know what performance upgrade would give me the best bang for my buck,

intake grate,
ride plate
impeller
flame arrestor

which of these will give me better results ?
also if i get the flame arrestors like k&N or something do i need to re jet and should i worry about water getting in through the air intake?
I dont want to buy a bunch of parts yet also would porting the exhaust help?