It's not a bad list of suggestions at all. But trying to categorize specific modules as more or less "important" is sorta pointless. Instead, you should look at a modular NOT as a collection of parts, but a bespoke SYSTEM that you've assembled, which has functions specific to your music. But if I answered the question literally, I'd say it was the power supply...and beyond that, the "importance" of modules really is something between you, your music, and the device itself.
-- Lugia
Sure, but outside the esoteric nature of 'connection,' there are obvious necessities when it comes to building a modular. It's the same thing as when building a guitar. There are going to be required parts, and the luthier (and maybe the customer) gets to put their own fresh take on that particular instrument. And as I appreciate Garfield's semi-scientific approach to categorizing and enumerating those vital parts, I am interested in his further elaboration of the concept. After all, if there is no such thing as importance in a modular build, then nobody really needs VCAs, do they?