Reddit reviews Designing and Tuning High-Performance Fuel Injection Systems

You could try a book. Personally, I used the hondata website and help files.

The basics aren't too bad if you are starting with a good map. If you have a terrible map I would try to find a good base one online or go to a professional tuner and buy an hour to get you started.

I've used one on a custom car we made in high school. It was (relatively) easy to fiddle with if you know what you're doing. If you want anything custom(sequential injection or coil on plug ignition), you're going to have to know how to solder. It's pretty good for turbo applications (IMO) because they have a pretty good boost control solenoid for relatively cheep that's easy to install and a built-in MAP sensor. A megasquirt is what I'm going to get when I do my KA-T build. They're also pretty expandable if you want to change anything later.

If you do decide to go the megasquirt route, I would suggest reading a book like this or this so you really know what in the hell you're doing when it comes time to "mess with the tables". It was pretty challenging on that custom car.

Also, Porsche is awesome.