a bit more background would be useful
what is your current recording setup? DAW and audio interface/mixer
do you want to integrate external instruments into your modular?
what sort of music are you intending to produce?
roughly where in the world are you? continent is probably good enough
some basics to get you started though:
effects could probably be handled quite well by a fx aid xl - replacing the afterneath or adding to it
in a tiny system like this envelopes can probably be handled by Pam's
mutable links is quite useful - it has 3 sections - a buffered mult (primarily for v/oct signals, but can be used for others), a mixer/buffered mult/precision adder, a 3 way mixer
mutable kinks is useful if you can find it - a rectifier (alters the shape of waveforms in various ways), simple logic circuit, sample and hold (with noise source - think semi-random value generator)
if you can't find a kinks then try to find a wmd/ssf toolbox - which has a variety of utilities in 6hp
happy nerding 3*MIA - which is a combination mixer, inverter, offset and attenuator again in 6hp
read through the manuals of all of these modules and try to cover as many of the functions as possible - you probably won't need (or at least won't think you need all of them) right now - but sooner or later you will
disting can cover quite a few - but only 1 at a time! so you can at least have a play with them to get a feel for what they do
smaller modules are not necessarily a good idea - whilst they do enable you to cram more functionality in to a smaller area, there is a huge trade of with ergonomics - often the better solution is (unfortunately) a bigger case
Utility modules are the inexpensive, dull polish that makes the expensive, shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities