Great, thanks! I will not bother with the AI for this build, nor worry about adding another VCO. I'll also have a look at some expression pedals.
My suggestion for the pedals themselves would be these: https://www.amazon.com/Sonicake-Vexpress-Passive-Expression-Effects/dp/B077PVVC38/ref=sr_1_6?crid=2WEX4FP0MNCKW&keywords=sonicake&qid=1658450499&sprefix=sonicake%2Caps%2C94&sr=8-6 I got one of these during the epic bout of pedal acquisition, figuring it was decent enough to use with my lap steel. Boy, was I surprised! It's built really well, takes up much less pedalboard space than the usual expression pedals, and it sounds smooth as silk...no weird pot jumps or crackles, and yes, it's all metal. No plastic case for these. But the killer thing is the price: $40!
Yeah, yeah...I know, Chinese pedal. Just try it.
1) when would an AI module be useful?
Input modules - if you are always using inputs and want to free up other amplification channels...
-- JimHowell1970
Also, it's generally a good idea to get an external audio input module that has an envelope follower. With that, you not only can preamp your instrument levels, but you can have a threshold-dependent gate output (comparator, basically) and the all-important EF itself, which extracts level information from your external signal and turns that into a CV signal for modulating all sorts of things. However, I think the Intellijel version is sort of lacking inasmuch as you've got both the input AND output on the same module, and that'll have a higher potential for cable snarling right around your build's I/O. Instead, use separate input and output modules, and I strongly suggest putting the input (I recommend the Doepfer A-119, actually) at the end of your oscillators, and treating it just like any old audio signal source (albeit with the added EF and comparator).
And then there's that Sonicsmith module that contains a pitch to voltage converter. P-V converters can be very fussy and troublesome (and WILL NOT put up with chords...monophonic lines ONLY), but if you were using something that's not a guitar (winds, f'rinstance). This was a huge part of the failure of Korg's X-911 "guitar synthesizer"...people couldn't wrap their heads around not being able to play chords, and when you do that with the X-911, the glitching becomes EPIC. But c. 1980...mmmm, not so much.