more modulation would be good - either lfos or envelope generators - even an ADSR if you want to use a keyboard or sequencer...

utilities would also be good , very good - clock dividers, sequential switches, attenuverters, a matrix mixer...

if it was me I'd want a whole extra row to fit these things in!!! and I'd use the 30hp free to add a couple of effects modules... especially for experimenting with delay/reverb before filtering & distortion...

"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