Assembling megasquirt doesn't require circuit level knowledge. You've got to be able to follow directions and must have significantly above average soldering skill. You'll learn something about electronics...

I've had two MS units for this project. The one that worked was from DIYAutotune.com

Really, any quality vendor should work if you provide specific instructions. Just make sure you get someone who will stand behind their work. It's a real pain to debug these things. I had to get an oscilloscope and it took a lot of time / frustration.

If you want to get rid of the stock dizzy, I recommend EDIS. It's a well proven system and very common. The components required to make it work are inexpensive. It's a crank trigger system, some fabrication required.

Removing the stock dizzy will result in a loss of tach function. I believe it will also result in a loss of AC function also (there is a circuit that detects minimum RPM for the compressor clutch). These functions can be turned back on, but require an additional "adapter" and some wiring.

For plug and play, I recommend VAST (stock ignition).
For a more serious application, I'd recommend EDIS and a coil bank.
MSD ignition is another common option, but it triggers off the stock dizzy.
Ignition is the most difficult part of these projects, IMHO.