I think you might need some more parts. Key antenna may require a new ignition switch and you might need the BIU. Only way to tell is to dig through the oem wiring manuals.
Usually people try to remove that junk

Many swap 04 usdm STi hardware when doing swaps.
I've played around with the idea of a software interlocker integrated into MerpMod. Basically, the user specifies an input sequence to pedals/cruise control that are required to start the car. It would have to be integrated into valet mode though, which has also been on my time-starved todo list.