i'm not going to answer the non-question above, but I will agree with Lugia about the 2hp (and 3hp) modules
I'd also look at Maths - especially the illustrated manual
a matrix mixer would also add an interesting way of mixing together modulation sources
a sequential switch
probably wouldn't add much in the way of extra voices
maybe something to drive the chord2 with - harmonaig possibly or a sinfonion (I have a sinfonion and use it a lot as a quantizer for marbles and to send chord pitch cv to a generalCV - you'll probably want an extra simple sequencer with this at some point - I use a pico seq - for changing song parts)
"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