veils for vcas - 4 vcas in 10hp - and actual amplifiers...
matrix mixers - Ive got a couple of DIY ones, but if I was going to get just one now I'd go for the doepfer due to ergonomics - if you want voltage control, then the 4ms VCAM
sequential switch - again the doepfer one is inexpensive and does what it says it does
logic - joranalogue compare2
also can't go wrong with happy nerding 3MIA (or their 3VCA), mutable kinks and links (or clones now they've been discontinued) or the WMD/SSF toolbox (if you can find one, again discontinued)
"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