the besst thing to do in many ways is to start with very little - ie a minimum viable synth... a sound source, a modulation source, a sound modifier, a way to play and a way to listen... plus maybe a basic utility...
so:
sound source - literally any will do - plaits clones are popular - as they have a lot of variety
modulation source - pams or maths are both great - although both complex (in different ways) - 1 is programmable with a simple menu system - the other is programmable with patch cables (this is a very powerful method and will transfer to all patching - see the 'maths illustrated supplement for further details - but really requires a lot of deep thought about what, when and how to get the most out of it)
a sound modifier - a low pass filter is a good start - doepfer make some inexpensive classics - moog, wasp, sem etc... and a multifx is another useful choice if you want to push the boat out a bit further - I'd go fx aid pro (screen exponentially improves the user experience)
a way to play - if the modulation source is Pams - then that can be a good start - it can do quantized stepped random pitch - otherwise it really depends on you...
a way to listen - a quad cascading vca such as a veils clone is a great starting point, although probably mono - which isn't really that big a deal - it will do the job and always be useful!
an utility - a module that can do attenuation/inversion/offset/mixing is also a good investment - possibly the best is the happy nerding 3 * mia - but there are others...
learn these modules inside and out and once you have done that (probably weeks, if not months) start adding slowly, 1 or 2 modules at a time, and repeating... try to keep a note of what you are missing as you go...
hope this helps...
"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