I think this project will be much more successful if you ditch the downpipe and go with headers. It's well worth the peace of mind, and will also open the door to future modding. You might be able to get away with just a downpipe, but when the car is tuned, the AFR will need to be richer or the timing will need to be reduced to eliminate the KR. This won't be good for performance.
Don't put too much thought/money into the intake system. A cone on the throttle body works great. CAI kits for this platform look cool, but performance wise, they are mostly a placebo.
