Stage 2 technically just requires a DP. However, most people go with a turboback anyways. As for the intake, the SPT is not supposed to screw with the A/F readings at all compared to stock (its designed by Subaru!), so I'd say you're good.

Whoever the guy was on here who had that really bad wreck in his WRB bugeye wagon (JD?) had a cutout, got to hear it at an auto-x. Sounded AWESOME. Definately made me think about taking off my catback for auto-x events