re serge: you can always buy them from random*source in modules - one at a time - some are available DIY too - but might not be for long - otherwise there's Elby in Australia that do serge like stuff iirc!
when I see building blocks I mainly think basic functions - lfos, vcos, filters, delays and a shed load of utility modules - something that you can use to 'patch anything up with' if you know what I mean...
"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