I fear you are pretty much on your own on this one, an LS1 in a WRX is not anywhere near the realm of normalcy for us to know what you have and have not done. Wiring up a swap like that can be a nightmare.
Have you hooked the LS1 alternator wire to the battery? That is kinda important, and you'll want to hook the starter up to the battery as well. I'm not sure about this, but the car may require some kind of signal back from the starter before allowing spark. You've definitely missed something somewhere, or have cut into something you shouldn't have, if your interior lights aren't working.