Injectors are extremely easy to source for the 3.0/3.6 - only needed if you want to experience the joys of boost safely. As mentioned - STI injectors slip straight in.
The OEM ignition coils punch out solid sparks, they ignite boosted engines very reliably, the Subaru coil is solid.
The path to NA power is in the airfilter/intake system to the throttle body, its in the headers and correct exhaust system and finally its in the tuning of the ECU. You upgrade all those items and you will get the solid gains mentioned by others. Proven and safe path with solid satisfaction