another thing to consider is that a 'modular effects rack' is effectively a full blown modular synthesizer, with the sound sources replaced by external ones - which generally means you need an input module of some kind to import the sound sources
this means that modulation and utilities are just as important in an effects rack as in a regular synth - don't skimp on the most important stuff (modulation and utilities)
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities