Which MegaSquirt are you planning on using? If you haven't purchased yet I would encourage you to take a hard look at the MS3-Pro or MS3-Pro Ultimate systems they offer. The Ultimate version will give you more I/O expansion capability.
The MS3-Pro family is the poor mans Haltech / Motec alternative. To be fair both Haltech and Motec will do things the MS3-Pro units do not do (right now). That said you will probably only use 60% or less of the MS3-Pro's capabilities.
The systems are very easy to install and easy to tune. There is a self learning capability to get you out of the blocks fast and then the ability to finesse the tune to get it just the way you want.
A very special nicety is the ability to use anyone's sensors and provide the sensor calibration to the ECU so you don't have to buy rebranded OEM sensors at high price premiums just because of the naming sticker on the sensor and the fact the ECU will not allow you to recalibrate for other sensors.
When you go EFI many people will use a tuning service or buy a day's worth of dyno time. If you get EGT sensors and use good Wideband O2 sensors (NTK) you can easily tune the car yourself without the dyno and save the $1,000 -1,200 of dyno time or whatever the tuning shop charges.
The MS3Pro system uses trim tables in closed loop to home in on the commanded lambda or AFR you specify. Once the trim tables have done their job you can look at the tune and quickly see where it 'wanted to be' and revise your tune to reflect the changes.
When you buy go to
DIYAutotune.com to buy. they are the retail face of Megasquirt and have literally everything you will need to implement the EFI system on your car. They also provide a very good support forum on the web for the system.
I think you will like your new EFI ECU choice in the extreme.
Ed