Hey Aus, I'm also in the same position as you. I really, really want to get Megasquirt (or Microsquirt) running on my car, but it's a TON of information to digest, and it's intimidating. I've been emailing back and forth with an old friend I used to run rally cross with, who has his old Escort running on MS3. I've been picking his brain and trying to figure out specifics. One of these days when I've got the time, I'm going to write up everything that seems pertinent, post it to the DIY Auto Tune forums, and let those guys pick it apart and correct it all. Once they're done, I should have a good idea of how to go about installing the Megasquirt.
At that point, I'll post parts lists, instructions, and pictures over here. As well as the results once I'm all done.
If you're going to go ahead and try to get it to work, I definitely suggest reading as much as you can on the thing. It's not complicated per se, but there is a lot going on and you'll need to understand it if you want to get the full potential out of it. There's all kinds of goodies you can do with it up an running. No lift shift, anti-lag, launch control, sequential injection, etc. Even just being able to datalog will be huge, especially for you running that giant turbo. On that note, there's also really good knock control and mitigation functionality in Tuner Studio.
If you buy this, keep us posted on how the install and setup goes. I'd love to see someone have it working in their Capri before I jump into it.