midi to cv you might want to look at the cv.ocd or if you want it in the rack erica synths are now making the mutant brain
Maths - best Maths substitute is Maths - simply because of the numerous videos on youtube and the fucking fantastic "maths illustrated supplement" - why is it so fantastic - because aside from giving you 32 patch examples for Maths - if you think hard about what, why and how maths and the patching is working it will serve as a jumping off point for all your future patching - what if I do this, how do I do this, why an I doing this?????
there are many other similar modules - designs based on the serge dual universal signal generator - but Maths is by far the most popular and in many ways the best - not least the ergonomics are good and the configuration - 2 function generators, 2 attenuverters with offsets, a bit of mixing (including a negative output) and a bit of logic are enough to kick start an entry level modular...
& don't let the name 'maths' put you off - you are after all designing/building yourself a customised, analog computer that specializes in generating sound - ie a modular synthesizer
"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