hehe, right sorry i was in bela land...(i looked at implementing my controller in bela)
about documentation and stuff. i was in the same situation as you a few years back. i always thought, why is this not well documented etc. i for one find the 3 string thingy on GitHub is in fact VERY well documented. but i know more about circuits than i did a few years back. so, you have to start with the simple stuff, buy one or two efx to solder from companies, with schematics and build plan. learn the basics. then from there the not so well documented stuff will be clearer. the same goes for code. look at the examples in arduino, do some very simple stuff and take it from there. i had to dive into that 3string code for some days before understanding every bit of it. the thing with diy controllers or instruments is this (at least for me) i have a very specific need and i cannot buy this controller. so i build it on my own. it is however very specialised and reacts according to my needs. i can share my code, i can write a little howto, measure the resistor values i used (i forgot what i used) but i cannot give support further than this, because i simply don't have the time as a full time musician, father etc... i guess this situation is the same for all others as well.
one example: since i built this controller as (bass)-controller for electronic music i did not care too much about velocity so i implemented a very rough mode only, that reduces latency considerably. maybe someone else wants to play synth pads with this thing and needs velocity to be very well behaved. that would be a big change in code though etc.
that all being said, i will upload the code to GitHub and write a small howto, add in all the hardware components.
it is really only:
a resistor per soft pot
a resistor per fsr
joystick and buttons can be hooked up without resistors (internal pull-ups)