I would skip the Perrin short shifter...and get the TIC/Karboy short shift lever combo with bushings:
TiC 08 Impreza Super Shifter Set Turn In Concepts
This combo comes with all the bushings, lever, etc. IMHO that is your best bet.
Also, I don't particularly like the placement of the Perrin Gauge pack (it kinda blocks/clutters up your stock gauges. IMHO some Autometer gauges and a clock pod or an A-pillar pod would better. Check JSC Speed: Performance Parts Warehouse
they have various gauges and mounting solutions. Personally, have the ATI clock pod, Autometer Boost and Oil Pressure Gauges, and AEM UEGO (wideband O2/AFR gauge). I would just verify any pod/mounting solution you get fits the '09 WRX, as I am unsure if there is any changes in the A-pillar design of the newer WRXs.
This is more of a personal taste thing...I think the Invidia N1 Racing Exhaust is UGLY as hell. Big fart tip, with the blue titanium look = super ricey. Not to mention the Racing version is very loud due to not having a resinator. If you are set on that look then I would conisider the Invidia N1 'Regular'. Personally, for the '08+ WRX I like the look of the Cobb, Borla, or Turbo XS catbacks MUCH more.
Additionally, I would upgrade the catback and DP at the same time, b/c IMHO the catback is worthless w/o the DP. Lastly, If you plan on going past Stage 2 the Cobb AP is a waste. If you are going to do a custom tune you might as well save the $700 on the Cobb AP and put that towards a custom open source tune w/dyno time.