you really can never have too many vcas - watch the mylarmelodies video on youtube called "why you can never have too many vcas"
6u/104 is still a small modular!!! it won't fit in your handbag - but it is portable etc etc
always allow space to expand - you might not think you will want to expand from this now but you probably will - if your case is full that means buying another case - a bigger case to start with will work out cheaper overall
why filters: so you can stick a filter between morphagene and monsoon for example
why kinks: modify modulation - stop it being boring - the current rack is basically one patch - kinks will add a lot to it
why fx aid: so you have choices about how to route stuff - add layers etc etc
as for a modulation source - pams is great (i believe) but not so hands on - personally I like maths - its sort of a microcosm of modular - see the "maths illustrated manual" online to see why
personally I'm not that big a fan of ochd - no control really
modulation is quite personal though - it's a journey not an end - some things you have to work out yourself
"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