Originally posted by Wishiwasfast- How is the idle control with the added circuit?

You're talking about the stepper motor IAC control, correct? If so, it works pretty well.

Originally posted by Wishiwasfast- What do I need for it to read the EGT, besides the sensor itself?

You need a specialized circuit to amplify the minuscule signal from the thermocouple. With the right parts, you can build one yourself or you can order an pre-built module. Google "megasquirt EGT interface" to find more information.

Originally posted by Wishiwasfast- Is this realistic?

Yes, but you should consider the cost. An MS3 ECU, plus the MS3X expansion board, costs quite a bit more than $400; more in the neighborhood of $600 to $700 for everything you mentioned. It's still cheaper and more versatile than DSMLink, but it's not quite as cheap as you expected.