Buy an 05 if you can. 1/2" wider wheels, STi logo on the BBS's, better bolt pattern, wider rear fenders, better steering rack, better interior, better seats, 3 spoke black steering wheel, helical front differential, stereo stock, red instead of pink badges, blacked out headlights, boost creep fixed, aluminum suspension components rather than steel stamped ones.
Simple bolt-ons work great for the car. You'll need a fuel pump if you plan on modifying since the stock injectors are at 90%+ duty cycle. I put down 308WHP/328WTQ with 255lph pump, TBE, APS CAI, and ECUtek ECU. Making anymore power costs A LOT. It's an ultimate daily with torque across the board, but if you want to get crazy buy an EVO instead.