You will be nuts if you dont buy those parts for $4500
But ya, all of those issues with the starter, awd conversion, and ECU are true. The part that isnt true is that the 5-speed WONT help the 1.8. A manual 1.8 is as fast as an auto 2.2, so thats at least worth it... Finding a manual ECU for a 1.8 shouldnt be TOO hard with all the swaps people are doing into older imprezas now, and find a used starter too and it should make it more worth while.
The wiring part... Ill let someone else answer
Im not big on wiring too