After mass purchasing what I figured were all of the parts I could possibly need for the project, I got down to soldering.
The specific megasquirt kit I bought was the MS-II PCB3.0 kit w/ case:
It comes with all of the components, meticulously organized and labeled, to fully assemble the ECU. Just add solder, and time.
I also highly recommend the unfortunately named "stimulator" for testing your circuits as you go:
The stim is also a good warmup soldering project if you're new to soldering or haven't done it in a while. It's best to practice on something smaller and less consequential than your ECU if it's been a while since the last time you soldered a PCB.
I actually also bought the MS Relay board, but as I'll address in a future post I think that was a big mistake. The relay board is just an added complexity / failure point and is difficult to rule out when you're tracking down electrical noise, etc.
[it's also possible to buy all of these things preassembled, for slightly more money. But where's the fun in that?]
Anyway. The assembly went very smoothly for me. I used the instructions from megamanual.com but later ended up getting most of my information from the forums at msextra.com. In retrospect, I would recommend sticking with one documentation source, to avoid running in to conflicting information. Therefore, because it's a more active community, I recommend sticking with documentation from http://www.msextra.com starting with the build guide here:
There are a few choices that must be made at build time. I've gone back and unsoldered things several times but the ones I settled on are:
--low-power, logic-level spark outputs driven from the D14 and D16 LED signals as described here: http://msextra.com/doc/general/sparkout-v30.html
--VR Sensor trigger input
--4-wire stepper-motor idle control
I've got a few pictures from the process of soldering up my MS board, but I think the pictures in the build manual are more helpful anyway so I'm not gonna bother posting mine unless anyone has questions.