I did this swap a few months ago and it worked out great. I also had a little trouble finding good info on this project and spent many long nights of sifting through pages of useless info.
List of items I used:
2005 EVO 8 ECU
Tactrix 1.3 flash cable
New OEM EVO 8 Knock sensor
2G Turbo ECU Pigtails re-pinned to EVO locations
1G ECU (cut connector off board)
OBDII Port (cut out of junkyard)
Optional but cheap and no tuning required
EVO 8 MAF
EVO 8 Injectors
I had a lot of time spent double checking pin out diagrams and found this one to be a good starting point. There are many options for wiring since you can choose to run ECU controlled boost, adapt for speed density and other cool features.
The big change I made was for idle control and all you have to do is swap the 2 b coil wires as they need to be reversed for the EVO ECU to control idle. Other than that I just flashed a stock map into the ECU, disabled the immobilizer and emissions controls and the car started right up. I will have to find my map on my computer and post it up for reference, the only code it throws is for the alternator circuit because an EVO alternator is ECU controlled. I feel like this is one of the best mods you can do since it is the cheapest stand alone style setup. I am not a fan of anything based off the stock ECU when you can run something this much better. To answer the questions above:
1. Which ECU did you use? I know the 3G Eclipse (4-cylinder, MT, Fed-spec) and base model Lancer have the same unit as the Evo 8, which opens up some more options to people searching for what is the most expensive piece of this puzzle. (Same hardware, software is flashed.)
EVO 8, I got mine for next to nothing but I think you can flash a turbo map into a non turbo lancer ECU.
2. Did you hardwire the new ECU in or build an adapter harness? Any tips? I'm on the fence about an adapter harness or making the swap permanent.
I made an adapter so I can remove it if needed
3. How did you get your first "tune" in place? Download it somewhere? Flash it yourself? What cable did you use? And do those cables for flashing OBDII Evos connect up to the OBDI port on our cars?
I downloaded a stock map, modified it and then flashed it into the ECU once it was installed in my car using the Tactrix cable. The Tactrix cable will log via the OBDII port.
Peter