the exhaust is a good idea, buschur racing, vrs racing and rnr racing all make cheap, high quality turbo back exhaust. youll probably hit 14 psi with just the mods you have listed; a guy i know has a talon tsi and it buries the 14 psi turbo gauge with just a kn filter, downpipe and muffler tip. my laser hits 13 with just a kn filter, before i put that on it hit 12. to get the car in the low 13, high 12s, follow this dsm upgrade sequence:
http://www.buschurracing.com/stage_1.html